SQL Server Interview Questions And Answers.

1. Which TCP/IP port does SQL Server run on? How can it be changed?

SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties.

2. What are the difference between clustered and a non-clustered index?

A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
A non clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a non clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.

3. What are the different index configurations a table can have?

A table can have one of the following index configurations:

No indexes
A clustered index
A clustered index and many nonclustered indexes
A nonclustered index
Many nonclustered indexes

4. What are different types of Collation Sensitivity?

Case sensitivity - A and a, B and b, etc.
Accent sensitivity
Kana Sensitivity - When Japanese kana characters Hiragana and Katakana are treated differently, it is called Kana sensitive.
Width sensitivity - A single-byte character (half-width) and the same character represented as a double-byte character (full-width) are treated differently than it is width sensitive.

5. What is OLTP (Online Transaction Processing)?

In OLTP - online transaction processing systems relational database design use the discipline of data modeling and generally follow the Codd rules of data normalization in order to ensure absolute data integrity. Using these rules complex information is broken down into its most simple structures (a table) where all of the individual atomic level elements relate to each other and satisfy the normalization rules.

6. What's the difference between a primary key and a unique key?

Both primary key and unique key enforces uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.

7. What is difference between DELETE and TRUNCATE commands?

Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command.

TRUNCATE:
1. TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.
2. TRUNCATE removes the data by deallocating the data pages used to store the table's data, and only the page deallocations are recorded in the transaction log.
3. TRUNCATE removes all rows from a table, but the table structure, its columns, constraints, indexes and so on, remains. The counter used by an identity for new rows is reset to the seed for the column.
4. You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint. Because TRUNCATE TABLE is not logged, it cannot activate a trigger.
5. TRUNCATE cannot be rolled back.
6. TRUNCATE is DDL Command.
7. TRUNCATE Resets identity of the table
DELETE:
1. DELETE removes rows one at a time and records an entry in the transaction log for each deleted row.
2. If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement.
3. DELETE Can be used with or without a WHERE clause
4. DELETE Activates Triggers.
5. DELETE can be rolled back.
6. DELETE is DML Command.
7. DELETE does not reset identity of the table.

Note: DELETE and TRUNCATE both can be rolled back when surrounded by TRANSACTION if the current session is not closed. If TRUNCATE is written in Query Editor surrounded by TRANSACTION and if session is closed, it can not be rolled back but DELETE can be rolled back.

8. When is the use of UPDATE_STATISTICS command?

This command is basically used when a large processing of data has occurred. If a large amount of deletions any modification or Bulk Copy into the tables has occurred, it has to update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.

9. What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?

They specify a search condition for a group or an aggregate. But the difference is that HAVING can be used only with the SELECT statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause. Having Clause is basically used only with the GROUP BY function in a query whereas WHERE Clause is applied to each row before they are part of the GROUP BY function in a query.

10. What are the properties and different Types of Sub-Queries?

Properties of Sub-Query
1. A sub-query must be enclosed in the parenthesis.
2. A sub-query must be put in the right hand of the comparison operator, and
3. A sub-query cannot contain an ORDER-BY clause.
4. A query can contain more than one sub-query.
Types of Sub-Query
1. Single-row sub-query, where the sub-query returns only one row.
2. Multiple-row sub-query, where the sub-query returns multiple rows,. and
3. Multiple column sub-query, where the sub-query returns multiple columns

11. What is SQL Profiler?

SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft SQL Server. You can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures are hampering performances by executing too slowly.
Use SQL Profiler to monitor only the events in which you are interested. If traces are becoming too large, you can filter them based on the information you want, so that only a subset of the event data is collected. Monitoring too many events adds overhead to the server and the monitoring process and can cause the trace file or trace table to grow very large, especially when the monitoring process takes place over a long period of time.

12. What are the authentication modes in SQL Server? How can it be changed?

Windows mode and Mixed Mode - SQL and Windows. To change authentication mode in SQL Server click Start, Programs, Microsoft SQL Server and click SQL Enterprise Manager to run SQL Enterprise Manager from the Microsoft SQL Server program group. Select the server then from the Tools menu select SQL Server Configuration Properties, and choose the Security page.

13. Which command using Query Analyzer will give you the version of SQL server and operating system?

SELECT SERVERPROPERTY ('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY ('edition').

14. What is SQL Server Agent?

SQL Server agent plays an important role in the day-to-day tasks of a database administrator (DBA). It is often overlooked as one of the main tools for SQL Server management. Its purpose is to ease the implementation of tasks for the DBA, with its full- function scheduling engine, which allows you to schedule your own jobs and scripts.

15. Can a stored procedure call itself or recursive stored procedure? How much level SP nesting is possible?

Yes. Because Transact-SQL supports recursion, you can write stored procedures that call themselves. Recursion can be defined as a method of problem solving wherein the solution is arrived at by repetitively applying it to subsets of the problem. A common application of recursive logic is to perform numeric computations that lend themselves to repetitive evaluation by the same processing steps. Stored procedures are nested when one stored procedure calls another or executes managed code by referencing a CLR routine, type, or aggregate. You can nest stored procedures and managed code references up to 32 levels.

16. What is Log Shipping?

Log shipping is the process of automating the backup of database and transaction log files on a production SQL server, and then restoring them onto a standby server. Enterprise Editions only supports log shipping. In log shipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db and can be used this as the Disaster Recovery plan. The key feature of log shipping is that it will automatically backup transaction logs throughout the day and automatically restore them on the standby server at defined interval.

17. Name 3 ways to get an accurate count of the number of records in a table?

SELECT * FROM table1 

SELECT COUNT(*) FROM table1 

SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid < 2

18. What does it mean to have QUOTED_IDENTIFIER ON? What are the implications of having it OFF?

When SET QUOTED_IDENTIFIER is ON, identifiers can be delimited by double quotation marks, and literals must be delimited by single quotation marks. When SET QUOTED_IDENTIFIER is OFF, identifiers cannot be quoted and must follow all Transact-SQL rules for identifiers.

19. What is the difference between a Local and a Global temporary table?

A local temporary table exists only for the duration of a connection or, if defined inside a compound statement, for the duration of the compound statement.
A global temporary table remains in the database permanently, but the rows exist only within a given connection. When connection is closed, the data in the global temporary table disappears. However, the table definition remains with the database for access when database is opened next time.

20. What is the STUFF function and how does it differ from the REPLACE function?

STUFF function is used to overwrite existing characters. Using this syntax, STUFF (string_expression, start, length, replacement_characters), string_expression is the string that will have characters substituted, start is the starting position, length is the number of characters in the string that are substituted, and replacement_characters are the new characters interjected into the string. REPLACE function to replace existing characters of all occurrences. Using the syntax REPLACE (string_expression, search_string, replacement_string), where every incidence of search_string found in the string_expression will be replaced with replacement_string.

21. What is PRIMARY KEY?

A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.

22. What is UNIQUE KEY constraint?

A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.

23. What is FOREIGN KEY?

A FOREIGN KEY constraint prevents any actions that would destroy links between tables with the corresponding data values. A foreign key in one table points to a primary key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no primary keys with that value. The foreign key constraints are used to enforce referential integrity.

24. What is CHECK Constraint?

A CHECK constraint is used to limit the values that can be placed in a column. The check constraints are used to enforce domain integrity.

25. What is NOT NULL Constraint?

A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints.

26. How to get @@ERROR and @@ROWCOUNT at the same time?

If @@Rowcount is checked after Error checking statement then it will have 0 as the value of @@Recordcount as it would have been reset. And if @@Recordcount is checked before the error-checking statement then @@Error would get reset. To get @@error and @@rowcount at the same time do both in same statement and store them in local variable.
SELECT @RC = @@ROWCOUNT, @ER = @@ERROR

27. What is a Scheduled Jobs or What is a Scheduled Tasks?

Scheduled tasks let user automate processes that run on regular or predictable cycles. User can schedule administrative tasks, such as cube processing, to run during times of slow business activity. User can also determine the order in which tasks run by creating job steps within a SQL Server Agent job. E.g. back up database, Update Stats of Tables. Job steps give user control over flow of execution. If one job fails, user can configure SQL Server Agent to continue to run the remaining tasks or to stop execution.

28. What are the advantages of using Stored Procedures?

Stored procedure can reduced network traffic and latency, boosting application performance.
Stored procedure execution plans can be reused, staying cached in SQL Server's memory, reducing server overhead.
Stored procedures help promote code reuse.
Stored procedures can encapsulate logic. You can change stored procedure code without affecting clients.
Stored procedures provide better security to your data.

29. What is a table called, if it has neither Cluster nor Non-cluster Index? What is it used for?

Unindexed table or Heap. Microsoft Press Books and Book on Line (BOL) refers it as Heap. A heap is a table that does not have a clustered index and, therefore, the pages are not linked by pointers. The IAM pages are the only structures that link the pages in a table together. Unindexed tables are good for fast storing of data. Many times it is better to drop all indexes from table and then do bulk of inserts and to restore those indexes after that.

30. Can SQL Servers linked to other servers like Oracle?

SQL Server can be linked to any server provided it has OLE-DB provider from Microsoft to allow a link. E.g. Oracle has an OLE-DB provider for oracle that Microsoft provides to add it as linked server to SQL Server group.

31. What is BCP? When does it used?

BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the structures same as source to destination. BULK INSERT command helps to import a data file into a database table or view in a user-specified format.

32. How to implement one-to-one, one-to-many and many-to-many relationships while designing tables?

One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships. One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships. Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.

33. What is an execution plan? When would you use it? How would you view the execution plan?

An execution plan is basically a road map that graphically or textually shows the data retrieval methods chosen by the SQL Server query optimizer for a stored procedure or ad- hoc query and is a very useful tool for a developer to understand the performance characteristics of a query or stored procedure since the plan is the one that SQL Server will place in its cache and use to execute the stored procedure or query. From within Query Analyzer is an option called "Show Execution Plan" (located on the Query drop-down menu). If this option is turned on it will display query execution plan in separate window when query is ran again.

What are DMVs?

Dynamic management views (DMVs) and functions return server state information that can be used to monitor the health of a server instance, diagnose problems, and tune performance; that is, they let you see what is going on inside SQL Server. They were introduced in SQL Server 2005 as an alternative to system tables. One example is viewing operating system wait statistics via this query:

SELECT * FROM sys.dm_os_wait_stats;

Another example is examining current sessions, much like the sp_who2 command:

SELECT * FROM sys.dm_exec_sessions;

What are temp tables? What is the difference between global and local temp tables?

Temporary tables are temporary storage structures. You may use temporary tables as buckets to store data that you will manipulate before arriving at a final format. The hash (#) character is used to declare a temporary table as it is prepended to the table name. A single hash (#) specifies a local temporary table.

CREATE TABLE #tempLocal ( nameid int, fname varchar(50), lname varchar(50) )

Local temporary tables are available to the current connection for the user, so they disappear when the user disconnects.
Global temporary tables may be created with double hashes (##). These are available to all users via all connections, and they are deleted only when all connections are closed.

CREATE TABLE ##tempGlobal ( nameid int, fname varchar(50), lname varchar(50) )

Once created, these tables are used just like permanent tables; they should be deleted when you are finished with them. Within SQL Server, temporary tables are stored in the Temporary Tables folder of the tempdb database.

How are transactions used?

Transactions allow you to group SQL commands into a single unit. The transaction begins with a certain task and ends when all tasks within it are complete. The transaction completes successfully only if all commands within it complete successfully. The whole thing fails if one command fails. The BEGIN TRANSACTION, ROLLBACK TRANSACTION, and COMMIT TRANSACTION statements are used to work with transactions. A group of tasks starts with the begin statement. If any problems occur, the rollback command is executed to abort. If everything goes well, all commands are permanently executed via the commit statement.

What is the difference between a clustered and a nonclustered index?

A clustered index affects the way the rows of data in a table are stored on disk. When a clustered index is used, rows are stored in sequential order according to the index column value; for this reason, a table can contain only one clustered index, which is usually used on the primary index value.
A nonclustered index does not affect the way data is physically stored; it creates a new object for the index and stores the column(s) designated for indexing with a pointer back to the row containing the indexed values.
You can think of a clustered index as a dictionary in alphabetical order, and a nonclustered index as a book’s index.

What are DBCC commands?

Basically, the Database Consistency Checker (DBCC) provides a set of commands (many of which are undocumented) to maintain databases — maintenance, validation, and status checks. The syntax is DBCC followed by the command name. Here are three examples:
DBCC CHECKALLOC — Check disk allocation consistency.
DBCC OPENTRAN — Display information about recent transactions.
DBCC HELP — Display Help for DBCC commands.

What is the difference between truncate and delete?

Truncate is a quick way to empty a table. It removes everything without logging each row. Truncate will fail if there are foreign key relationships on the table. Conversely, the delete command removes rows from a table, while logging each deletion and triggering any delete triggers that may be present.

What does the NOLOCK query hint do?

Table hints allow you to override the default behavior of the query optimizer for statements. They are specified in the FROM clause of the statement. While overriding the query optimizer is not always suggested, it can be useful when many users or processes are touching data. The NOLOCK query hint is a good example because it allows you to read data regardless of who else is working with the data; that is, it allows a dirty read of data — you read data no matter if other users are manipulating it. A hint like NOLOCK increases concurrency with large data stores.

SELECT * FROM table_name (NOLOCK)

Microsoft advises against using NOLOCK, as it is being replaced by the READUNCOMMITTED query hint. There are lots more query hints with plenty of information online.

What is a CTE?

A common table expression (CTE) is a temporary named result set that can be used within other statements like SELECT, INSERT, UPDATE, and DELETE. It is not stored as an object and its lifetime is limited to the query. It is defined using the WITH statement as the following example shows:

WITH ExampleCTE (id, fname, lname)
AS
(
SELECT id, firstname, lastname FROM table
)
SELECT * FROM ExampleCTE

A CTE can be used in place of a view in some instances.

What is a view? What is the WITH CHECK OPTION clause for a view?

A view is a virtual table that consists of fields from one or more real tables. Views are often used to join multiple tables or to control access to the underlying tables.
The WITH CHECK OPTION for a view prevents data modifications (to the data) that do not confirm to the WHERE clause of the view definition. This allows data to be updated via the view, but only if it belongs in the view.

What is a query execution plan?

SQL Server has an optimizer that usually does a great job of optimizing code for the most effective execution. A query execution plan is the breakdown of how the optimizer will run (or ran) a query. There are several ways to view a query execution plan. This includes using the Show Execution Plan option within Query Analyzer; Display Estimated Execution Plan on the query dropdown menu; or use the SET SHOWPLAN_TEXT ON command before running a query and capturing the execution plan event in a SQL Server Profiler trace.

What does the SQL Server Agent Windows service do?

SQL Server Agent is a Windows service that handles scheduled tasks within the SQL Server environment (aka jobs). The jobs are stored/defined within SQL Server, and they contain one or more steps that define what happens when the job runs. These jobs may run on demand, as well as via a trigger or predefined schedule. This service is very important when determining why a certain job did not run as planned — often it is as simple as the SQL Server Agent service not running.

What is the default port number for SQL Server?

If enabled, the default instance of Microsoft SQL Server listens on TCP port 1433. Named instances are configured for dynamic ports, so an available port is chosen when SQL Server starts. When connecting to a named instance through a firewall, configure the Database Engine to listen on a specific port, so that the appropriate port can be opened in the firewall.
The list of possible questions is endless. I am sure these questions will spawn debate and discussion.

What is RDBMS?

Relational Data Base Management Systems (RDBMS) are database management systems that maintain data records and indices in tables. Relationships may be created and maintained across and among the data and tables. In a relational database, relationships between data items are expressed by means of tables. Interdependencies among these tables are expressed by data values rather than by pointers. This allows a high degree of data independence. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage. (Read more here)

What are the Properties of the Relational Tables?

Relational tables have the following six properties:

Values are atomic.
Column values are of the same kind.
Each row is unique.
The sequence of columns is insignificant.
The sequence of rows is insignificant.
Each column must have a unique name.

What is Normalization?

Database normalization is a data design and organization process applied to data structures based on rules that help building relational databases. In relational database design, the process of organizing data to minimize redundancy is called normalization. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.

What is De-normalization?

De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.

How is ACID property related to Database?

ACID (an acronym for Atomicity Consistency Isolation Durability) is a concept that Database Professionals generally look for while evaluating databases and application architectures. For a reliable database, all this four attributes should be achieved.
Atomicity is an all-or-none proposition.
Consistency guarantees that a transaction never leaves your database in a half-finished state.
Isolation keeps transactions separated from each other until they are finished.
Durability guarantees that the database will keep track of pending changes in such a way that the server can recover from an abnormal termination. (Read more here)

What are the Different Normalization Forms?

1NF: Eliminate Repeating Groups
Make a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.
2NF: Eliminate Redundant Data
If an attribute depends on only part of a multi-valued key, then remove it to a separate table.
3NF: Eliminate Columns Not Dependent On Key
If attributes do not contribute to a description of the key, then remove them to a separate table. All attributes must be directly dependent on the primary key. (Read more here)
BCNF: Boyce-Codd Normal Form
If there are non-trivial dependencies between candidate key attributes, then separate them out into distinct tables.
4NF: Isolate Independent Multiple Relationships
No table may contain two or more 1:n or n:m relationships that are not directly related.
5NF: Isolate Semantically Related Multiple Relationships
There may be practical constrains on information that justify separating logically related many-to-many relationships.
ONF: Optimal Normal Form
A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.
DKNF: Domain-Key Normal Form
A model free from all modification anomalies is said to be in DKNF.
Remember, these normalization guidelines are cumulative. For a database to be in 3NF, it must first fulfill all the criteria of a 2NF and 1NF database.

What is a Stored Procedure?

A stored procedure is a named group of SQL statements that have been previously created and stored in the server database. Stored procedures accept input parameters so that a single procedure can be used over the network by several clients using different input data. And when the procedure is modified, all clients automatically get the new version. Stored procedures reduce network traffic and improve performance. Stored procedures can be used to help ensure the integrity of the database.
e.g. sp_helpdb, sp_renamedb, sp_depends etc.

What is a Trigger?

A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in and managed by the DBMS. Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed; DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be considered to be similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-drive and are not attached to a specific table as triggers are. Stored procedures are explicitly executed by invoking a CALL to the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.
Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself; so when the trigger is fired because of data modification, it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger. (Read more here)

What are the Different Types of Triggers?

There are two types of Triggers.
1) DML Trigger
There are two types of DML Triggers

1.Instead of Trigger
Instead of Triggers are fired in place of the triggering action such as an insert, update, or delete.

2. After Trigger
After triggers execute following the triggering action, such as an insert, update, or delete.

2) DDL Trigger
This type of trigger is fired against Drop Table, Create Table, Alter Table or Login events. DDL Triggers are always After Triggers.

What is a View?

A simple view can be thought of as a subset of a table. It can be used for retrieving data as well as updating or deleting rows. Rows updated or deleted in the view are updated or deleted in the table the view was created with. It should also be noted that as data in the original table changes, so does the data in the view as views are the way to look at parts of the original table. The results of using a view are not permanently stored in the database. The data accessed through a view is actually constructed using standard T-SQL select command and can come from one to many different base tables or even other views.

What is an Index?

An index is a physical structure containing pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name. The users cannot see the indexes; they are just used to speed up queries. Effective indexes are one of the best ways to improve performance in a database application. A table scan happens when there is no index available to help a query. In a table scan, the SQL Server examines every row in the table to satisfy the query results. Table scans are sometimes unavoidable, but on large tables, scans have a terrific impact on performance.

What is a Linked Server?

Linked Servers is a concept in SQL Server by which we can add other SQL Server to a Group and query both the SQL Server databases using T-SQL Statements. With a linked server, you can create very clean, easy–to-follow SQL statements that allow remote data to be retrieved, joined and combined with local data. Stored Procedures sp_addlinkedserver, sp_addlinkedsrvlogin will be used to add new Linked Server. (Read more here)

What is a Cursor?

A cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.
In order to work with a cursor, we need to perform some steps in the following order:

Declare cursor
Open cursor
Fetch row from the cursor
Process fetched row
Close cursor
Deallocate cursor (Read more here)

What is Collation?

Collation refers to a set of rules that determine how data is sorted and compared. Character data is sorted using rules that define the correct character sequence with options for specifying case sensitivity, accent marks, Kana character types, and character width.

What is an Identity?

Identity (or AutoNumber) is a column that automatically generates numeric values. A start and increment value can be set, but most DBAs leave these at 1. A GUID column also generates unique keys. Updated based on the comment of Aaron Bertrand. (Blog)

What is DataWarehousing?

Subject-oriented, which means that the data in the database is organized so that all the data elements relating to the same real-world event or object are linked together;
Time-variant, which means that the changes to the data in the database are tracked and recorded so that reports can be produced showing changes over time;
Non-volatile, which means that data in the database is never over-written or deleted, once committed, the data is static, read-only, but retained for future reporting.
Integrated, which means that the database contains data from most or all of an organization’s operational applications, and that this data is made consistent.

What languages BI uses to achieve the goal?

BI uses following languages for achieve the Goal.

MDX – Multidimensional Expressions:

This language is used for retrieving data from SSAS cubes. It looks very similar to T-SQL, but it is very different in the areas of conceptualization and implementation.

DMX – Data Mining Extensions:

This is again used for SSAS, but rather than cubes it is used for data mining structures. This language is more complicated than MDX. Microsoft has provided many wizards in its BI tools, which further reduced number of experts for learning this language, which deals with data mining structures.

XMLA – XML for Analysis:

This is mainly used for SSAS administrative tasks. It is quite commonly used in administration tasks such as backup or restore database, copy and move database, or for learning Meta data information. Again, MS BI tools provide a lot of wizards for the same. (Read More Here)

What is Standby Servers? Explain Types of Standby Servers.

Standby Server is a type of server that can be brought online in a situation when Primary Server goes offline and application needs continuous (high) availability of the server. There is always a need to set up a mechanism where data and objects from primary server are moved to secondary (standby) server. This mechanism usually involves the process of moving backup from the primary server to the secondary server using T-SQL scripts. Often, database wizards are used to set up this process.
Different types of standby servers are given as follows:

1) Hot Standby:

Hot Standby can be achieved in the SQL Server using SQL Server 2005 Enterprise Edition and the later enterprise versions. SQL Server 2005 has introduced Mirroring of database that can be configured for automatic failover in a disaster situation. In the case of synchronous mirroring, the database is replicated to both the servers simultaneously. This is a little expensive but provides the best high availability. In this case, both primary and standby servers have same data all the time.

2) Warm Standby:

In Warm Standby, automatic failover is not configured. This is usually set up using Log Shipping or asynchronous mirroring. Sometimes warm standby is lagging by a few minutes or seconds, which results into loss of few latest updates when the primary server fails and secondary server needs to come online. Sometimes a warm standby server that is lagging by a few transactions is brought back to the current state by applying the recent transaction log.

3) Cold Standby:

Code Standby servers need to be switched manually, and sometimes all the backups as well as the required OS need to be applied. Cold Standby just physically replaces the previous server.
(Read more here)

What is Dirty Read?

A dirty read occurs when two operations, say, read and write occur together giving the incorrect or unedited data. Suppose, A changed a row but did not committed the changes. B reads the uncommitted data but his view of the data may be wrong so that is Dirty Read.

Why can’t I use Outer Join in an Indexed View?

Rows can logically disappear from an indexed view based on OUTER JOIN when you insert data into a base table. This makes incrementally updating OUTER JOIN views relatively complex to implement, and the performance of the implementation would be slower than for views based on standard (INNER) JOIN.(Read More Here)

What is the Correct Order of the Logical Query Processing Phases?

The correct order of the Logical Query Processing Phases is as follows:

1. FROM
2. ON
3. OUTER
4. WHERE
5. GROUP BY
6. CUBE | ROLLUP
7. HAVING
8. SELECT
9. DISTINCT
10. TOP
11. ORDER BY

What are Different Types of Locks?

Shared Locks: Used for operations that do not change or update data (read-only operations), such as a SELECT statement.
Update Locks: Used on resources that can be updated. It prevents a common form of deadlock that occurs when multiple sessions are reading, locking, and potentially updating resources later.
Exclusive Locks: Used for data-modification operations, such as INSERT, UPDATE, or DELETE. It ensures that multiple updates cannot be made to the same resource at the same time.
Intent Locks: Used to establish a lock hierarchy. The types of intent locks are as follows: intent shared (IS), intent exclusive (IX), and shared with intent exclusive (SIX).
Schema Locks: Used when an operation dependent on the schema of a table is executing. The types of schema locks are schema modification (Sch-M) and schema stability (Sch-S).
Bulk Update Locks: Used when bulk-copying data into a table and the TABLOCK hint is specified.

What are Pessimistic Lock and Optimistic Lock?

Optimistic Locking is a strategy where you read a record, take note of a version number and check that the version hasn’t changed before you write the record back. If the record is dirty (i.e. different version to yours), then you abort the transaction and the user can re-start it.
Pessimistic Locking is when you lock the record for your exclusive use until you have finished with it. It has much better integrity than optimistic locking but requires you to be careful with your application design to avoid Deadlocks.

When is the use of UPDATE_STATISTICS command?

This command is basically used when a large amount of data is processed. If a large amount of deletions, modifications or Bulk Copy into the tables has occurred, it has to update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.

What is the Difference between a HAVING clause and a WHERE clause?

They specify a search condition for a group or an aggregate. But the difference is that HAVING can be used only with the SELECT statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause. Having Clause is basically used only with the GROUP BY function in a query, whereas WHERE Clause is applied to each row before they are part of the GROUP BY function in a query. (Read more here)

What is Connection Pooling and why it is Used?

To minimize the cost of opening and closing connections, ADO.NET uses an optimization technique called connection pooling.
The pooler maintains ownership of the physical connection. It manages connections by keeping alive a set of active connections for each given connection configuration. Whenever a user calls Open on a connection, the pooler looks for an available connection in the pool. If a pooled connection is available, it returns it to the caller instead of opening a new connection. When the application calls Close on the connection, the pooler returns it to the pooled set of active connections instead of closing it. Once the connection is returned to the pool, it is ready to be reused on the next Open call.

What are the Properties and Different Types of Sub-Queries?

Properties of a Sub-Query

A sub-query must be enclosed in the parenthesis.
A sub-query must be put on the right hand of the comparison operator, and
A sub-query cannot contain an ORDER BY clause, however sub-query can use ORDER BY when used with TOP clause. Read Comment by David Bridge
A query can contain more than one sub-query.

Types of Sub-query

Single-row sub-query, where the sub-query returns only one row.
Multiple-row sub-query, where the sub-query returns multiple rows, and
Multiple column sub-query, where the sub-query returns multiple columns

What is an SQL Profiler?

SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft SQL Server. You can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures are hampering performances by executing very slowly.
Use SQL Profiler to monitor only the events in which you are interested. If traces are becoming too large, you can filter them based on the information you want, so that only a subset of the event data is collected. Monitoring too many events adds overhead to the server and the monitoring process and can cause the trace file or trace table to grow very large, especially when the monitoring process takes place over a long period of time.

What are the Authentication Modes in SQL Server? How can it be Changed?

There are two authentication modes in SQL Server.

Windows Mode
Mixed Mode – SQL and Windows

To change authentication mode in SQL Server, go to Start -> Programs- > Microsoft SQL Server and click SQL Enterprise Manager to run SQL Enterprise Manager from the Microsoft SQL Server program group. Select the server; then from the Tools menu, select SQL Server Configuration Properties and choose the Security page.

Which Command using Query Analyzer will give you the Version of SQL Server and Operating System?

SELECT SERVERPROPERTY('Edition') AS Edition,

SERVERPROPERTY('ProductLevel') AS ProductLevel,

SERVERPROPERTY('ProductVersion') AS ProductVersion

GO

(Read more here)

What is an SQL Server Agent?

The SQL Server agent plays an important role in the day-to-day tasks of a database administrator (DBA). It is often overlooked as one of the main tools for SQL Server management. Its purpose is to ease the implementation of tasks for the DBA, with its full-function scheduling engine, which allows you to schedule your own jobs and scripts. (Read more here)

Can a Stored Procedure call itself or a Recursive Stored Procedure? How many levels of SP nesting is possible?

Yes. As T-SQL supports recursion, you can write stored procedures that call themselves. Recursion can be defined as a method of problem solving wherein the solution is arrived at by repetitively applying it to subsets of the problem. A common application of recursive logic is to perform numeric computations that lend themselves to repetitive evaluation by the same processing steps. Stored procedures are nested when one stored procedure calls another or executes managed code by referencing a CLR routine, type, or aggregate. You can nest stored procedures up to 32 levels. Any reference to managed code from a Transact-SQL stored procedure counts as one level against the 32-level nesting limit. Methods invoked from within managed code do not count against this limit. (Read more here) (Courtesy: Vinod Kumar)

What is Log Shipping?

Log shipping is the process of automating the backup of database and transaction log files on a production SQL server and then restoring them onto a standby server. All Editions (except Express Edition) supports log shipping. In log shipping, the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db and can be used this as the Disaster Recovery plan. The key feature of log shipping is that it will automatically backup transaction logs throughout the day and automatically restore them on the standby server at defined intervals. (Courtney: Rhys)

Name 3 ways to get an Accurate Count of the Number of Records in a Table?

SELECT * FROM table1
SELECT COUNT(*) FROM table1

SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid < 2

What does it mean to have QUOTED_IDENTIFIER ON? What are the Implications of having it OFF?

What is the Difference between a Local and a Global Temporary Table?

A local temporary table exists only for the duration of a connection, or if defined inside a compound statement, for the duration of the compound statement.
A global temporary table remains in the database accessible across the connections. Once the connection where original global table is declared dropped this becomes unavailable.

What is the STUFF Function and How Does it Differ from the REPLACE Function?

STUFF function is used to overwrite existing characters using this syntax: STUFF (string_expression, start, length, replacement_characters), where string_expression is the string that will have characters substituted, start is the starting position, length is the number of characters in the string that are substituted, and replacement_characters are the new characters interjected into the string. REPLACE function is used to replace existing characters of all occurrences. Using the syntax REPLACE (string_expression, search_string, replacement_string), every incidence of search_string found in the string_expression will be replaced with replacement_string.

What is PRIMARY KEY?

A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row, and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.

What is UNIQUE KEY Constraint?

A UNIQUE constraint enforces the uniqueness of the values in a set of columns; so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.

What is FOREIGN KEY?

What is CHECK Constraint?

A CHECK constraint is used to limit the values that can be placed in a column. The check constraints are used to enforce domain integrity. (Read more here)

What is NOT NULL Constraint?

A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints.
(Read more here)

What is the difference between UNION and UNION ALL?

UNION
The UNION command is used to select related information from two tables, much like the JOIN command. However, when using the UNION command all selected columns need to be of the same data type. With UNION, only distinct values are selected.
UNION ALL
The UNION ALL command is equal to the UNION command, except that UNION ALL selects all values.
The difference between UNION and UNION ALL is that UNION ALL will not eliminate duplicate rows, instead it just pulls all rows from all the tables fitting your query specifics and combines them into a table. (Read more here)

What is B-Tree?

The database server uses a B-tree structure to organize index information. B-Tree generally has following types of index pages or nodes:

Root node: A root node contains node pointers to only one branch node.
Branch nodes: A branch node contains pointers to leaf nodes or other branch nodes, which can be two or more.
Leaf nodes: A leaf node contains index items and horizontal pointers to other leaf nodes, which can be many.

How to get @@ERROR and @@ROWCOUNT at the Same Time?

If @@Rowcount is checked after Error checking statement, then it will have 0 as the value of @@Recordcount as it would have been reset. And if @@Recordcount is checked before the error-checking statement, then @@Error would get reset. To get @@error and @@rowcount at the same time, include both in same statement and store them in a local variable. SELECT @RC = @@ROWCOUNT, @ER = @@ERROR

What is a Scheduled Job or What is a Scheduled Task?

Scheduled tasks let user automate processes that run on regular or predictable cycles. User can schedule administrative tasks, such as cube processing, to run during times of slow business activity. User can also determine the order in which tasks run by creating job steps within a SQL Server Agent job, e.g. back up database and update statistics of the tables. Job steps give user control over flow of execution. If one job fails, then the user can configure SQL Server Agent to continue to run the remaining tasks or to stop execution.

What are the Advantages of Using Stored Procedures?

Stored procedure can reduced network traffic and latency, boosting application performance.
Stored procedure execution plans can be reused; they staying cached in SQL Server’s memory, reducing server overhead.
Stored procedures help promote code reuse.
Stored procedures can encapsulate logic. You can change stored procedure code without affecting clients.
Stored procedures provide better security to your data.

What is a Table Called, if it has neither Cluster nor Non-cluster Index? What is it Used for?

Unindexed table or Heap. Microsoft Press Books and Book on Line (BOL) refers it as Heap. A heap is a table that does not have a clustered index and therefore, the pages are not linked by pointers. The IAM pages are the only structures that link the pages in a table together. Unindexed tables are good for fast storing of data. Many times, it is better to drop all the indexes from table and then do bulk of INSERTs and restore those indexes after that.

Can SQL Servers Linked to other Servers like Oracle?

SQL Server can be linked to any server provided it has OLE-DB provider from Microsoft to allow a link, e.g. Oracle has an OLE-DB provider that Microsoft provides to add it as a linked server to the SQL Server group

What is BCP? When is it Used?

BCP or BulkCopy is a tool used to copy huge amounts of data from tables and views. BCP does not copy the complete structures from source to destination. BULK INSERT command helps to import a data file into a database table or view in a user-specified format.

What Command do we Use to Rename a db, a Table and a Column?

To Rename db

sp_renamedb ‘oldname’ , ‘newname
If someone is using db it will not accept sp_renmaedb. In that case, first bring db to single user mode using sp_dboptions. Use sp_renamedb to rename the database. Use sp_dboptions to bring the database to multi-user mode.
e.g.

USE MASTER;

GO

EXEC sp_dboption AdventureWorks, 'Single User', True

GO

EXEC sp_renamedb 'AdventureWorks', 'AdventureWorks_New'

GO

EXEC sp_dboption AdventureWorks, 'Single User', False

GO

To Rename Table

We can change the table name using sp_rename as follows:

sp_rename 'oldTableName' 'newTableName'

e.g.

sp_RENAME 'Table_First', 'Table_Last'

GO

To rename Column

The script for renaming any column is as follows:

sp_rename 'TableName.[OldcolumnName]', 'NewColumnName', 'Column'

e.g.

sp_RENAME 'Table_First.Name', 'NameChange' , 'COLUMN'

GO

What are sp_configure Commands and SET Commands?

Use sp_configure to display or change server-level settings. To change the database-level settings, use ALTER DATABASE. To change settings that affect only the current user session, use the SET statement.
e.g.

sp_CONFIGURE 'show advanced', 0

GO

RECONFIGURE

GO

sp_CONFIGURE

GO

You can run the following command and check the advanced global configuration settings.

sp_CONFIGURE 'show advanced', 1

GO

RECONFIGURE

GO

sp_CONFIGURE

GO

(Read more here)

How to Implement One-to-One, One-to-Many and Many-to-Many Relationships while Designing Tables?

One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships. One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.
Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.

What is Difference between Commit and Rollback when Used in Transactions?

The usual structure of the TRANSACTION is as follows:
BEGIN TRANSACTION
Operations
COMMIT TRANSACTION or ROLLBACK TRANSACTION
When Commit is executed, every statement between BEGIN and COMMIT becomes persistent to database. When Rollback is executed, every statement between BEGIN and ROLLBACK are reverted to the state when BEGIN was executed.

What is an Execution Plan? When would you Use it? How would you View the Execution Plan?

An execution plan is basically a road map that graphically or textually shows the data retrieval methods chosen by the SQL Server query optimizer for a stored procedure or ad-hoc query, and it is a very useful tool for a developer to understand the performance characteristics of a query or stored procedure since the plan is the one that SQL Server will place in its cache and use to execute the stored procedure or query. Within the Query Analyzer, there is an option called “Show Execution Plan” (in the Query drop-down menu). If this option is turned on, it will display query execution plan in a separate window when the query is ran again.

What is Difference between Table Aliases and Column Aliases? Do they Affect Performance?

Usually, when the name of the table or column is very long or complicated to write, aliases are used to refer them.
e.g.
SELECT VeryLongColumnName col1
FROM VeryLongTableName tab1
In the above example, col1 and tab1 are the column alias and table alias, respectively. They do not affect the performance at all.

What is the difference between CHAR and VARCHAR Datatypes?

VARCHARS are variable length strings with a specified maximum length. If a string is less than the maximum length, then it is stored verbatim without any extra characters, e.g. names and emails. CHARS are fixed-length strings with a specified set length. If a string is less than the set length, then it is padded with extra characters, e.g. phone number and zip codes. For instance, for a column which is declared as VARCHAR(30) and populated with the word ‘SQL Server,’ only 10 bytes will be stored in it. However, if we have declared the column as CHAR(30) and populated with the word ‘SQL Server,’ it will still occupy 30 bytes in database.

What is the Difference between VARCHAR and VARCHAR(MAX) Datatypes?

VARCHAR stores variable-length character data whose range varies up to 8000 bytes; varchar(MAX) stores variable-length character data whose range may vary beyond 8000 bytes and till 2 GB. TEXT datatype is going to be deprecated in future versions, and the usage of VARCHAR(MAX) is strongly recommended instead of TEXT datatypes.

What is the Difference between VARCHAR and NVARCHAR datatypes?

In principle, they are the same and are handled in the same way by your application. The only difference is that NVARCHAR can handle unicode characters, allowing you to use multiple languages in the database (Arabian, Chinese, etc.). NVARCHAR takes twice as much space when compared to VARCHAR. Use NVARCHAR only if you are using foreign languages.

Which are the Important Points to Note when Multilanguage Data is Stored in a Table?

There are two things to keep in mind while storing unicode data. First, the column must be of unicode data type (nchar, nvarchar, ntext). Second, the value must be prefixed with N while insertion. For example,
INSERT INTO table (Hindi_col) values (N’hindi data’)

How to Optimize Stored Procedure Optimization?

There are many tips and tricks for the same. Here are few:

Include SET NOCOUNT ON statement.
Use schema name with object name.
Do not use the prefix “sp_” in the stored procedure name.
Use IF EXISTS (SELECT 1) instead of (SELECT *).
Use the sp_executesql stored procedure instead of the EXECUTE statement.
Try to avoid using SQL Server cursors whenever possible.
Keep the Transaction as short as possible.
Use TRY-Catch for error handling.

(Read more here)

What is SQL Injection? How to Protect Against SQL Injection Attack?

SQL injection is an attack in which malicious code is inserted into strings that are later passed to an instance of SQL Server for parsing and execution. Any procedure that constructs SQL statements should be reviewed for injection vulnerabilities because SQL Server will execute all syntactically valid queries that it receives. Even parameterized data can be manipulated by a skilled and determined attacker.
Here are few methods which can be used to protect again SQL Injection attack:

Use Type-Safe SQL Parameters
Use Parameterized Input with Stored Procedures
Use the Parameters Collection with Dynamic SQL
Filtering Input parameters
Use the escape character in LIKE clause
Wrapping Parameters with QUOTENAME() and REPLACE()

How to Find Out the List Schema Name and Table Name for the Database?

We can use following script:

SELECT '['+SCHEMA_NAME(schema_id)+'].['+name+']' AS SchemaTable

FROM sys.tables

(Read more here)

What is CHECKPOINT Process in the SQL Server?

CHECKPOINT process writes all dirty pages for the current database to disk. Dirty pages are data pages that have been entered into the buffer cache and modified, but not yet written to disk.

How does Using a Separate Hard Drive for Several Database Objects Improves Performance Right Away?

A non-clustered index and tempdb can be created on a separate disk to improve performance.
(Read more here)

How to Find the List of Fixed Hard Drive and Free Space on Server?

We can use the following Stored Procedure to figure out the number of fixed drives (hard drive) a system has along with free space on each of those drives.
EXEC master..xp_fixeddrives

Why can there be only one Clustered Index and not more than one?

Cluster Index physically stores data, or arranges data in one order (depends on which column(s) you have defined Clustered index and in which order).
As a fact, we all know that a set of data can be only stored in only one order; that is why only one clustered index is possible.(Read more here)

What is Difference between Line Feed (\n) and Carriage Return (\r)?

Line Feed – LF – \n – 0x0a – 10 (decimal)
Carriage Return – CR – \r – 0x0D – 13 (decimal)

DECLARE @NewLineChar AS CHAR(2) = CHAR(13) + CHAR(10)

PRINT ('SELECT FirstLine AS FL ' +@NewLineChar + 'SELECT SecondLine AS SL' )

(Read more here)

Is It Possible to have Clustered Index on Separate Drive From Original Table Location?

No! It is not possible. (Read more here)

What is a Hint?

Hints are options and strong suggestions specified for enforcement by the SQL Server query processor on DML statements. The hints override any execution plan the query optimizer might select for a query.(Read more here)
There are three different types of hints. Let us understand the basics of each of them separately.

Join Hint

This hint is used when more than one table is used in a query. Two or more tables can be joined using different types of joins. This hint forces the type of join algorithm that is used. Joins can be used in SELECT, UPDATE and DELETE statements.

Query Hint

This hint is used when certain kind of logic has to be applied to a whole query. Any hint used in the query is applied to the complete query as opposed to a part of it. There is no way to specify that only a certain part of a query should be used with the hint. After any query, the OPTION clause is specified to apply the logic to this query. A query always has any of the following statements: SELECT, UPDATE, DELETE, INSERT or MERGE (SQL 2K8); and this hint can be applied to all of them.

Table Hint

This hint is used when certain kind of locking mechanism of tables has to be controlled. SQL Server query optimizer always puts the appropriate kind of lock on tables, when any of the Transact SQL operations SELECT, UPDATE, DELETE, INSERT or MERGE is used. There are certain cases when the developer knows when and where to override the default behavior of the locking algorithm, and these hints are useful in those scenarios. (Read more here)

How to Delete Duplicate Rows?

We can delete duplicate rows using CTE and ROW_NUMBER () feature of SQL Server 2005 and SQL Server 2008.
e.g.

WITH CTE (COl1,Col2, DuplicateCount)

AS

(

SELECT COl1,Col2,

ROW_NUMBER() OVER(PARTITION BY COl1,Col2 ORDER BY Col1) AS DuplicateCount

FROM DuplicateRcordTable

)

DELETE

FROM CTE

WHERE DuplicateCount >1

(Read more here)

Why the Trigger Fires Multiple Times in Single Login?

It happens because multiple SQL Server services are running and also as intellisense is turned on.

What is Aggregate Functions?

Aggregate functions perform a calculation on a set of values and return a single value. Aggregate functions ignore NULL values except COUNT function. HAVING clause is used, along with GROUP BY for filtering query using aggregate values.
The following functions are aggregate functions.
AVG, MIN, CHECKSUM_AGG, SUM, COUNT, STDEV, COUNT_BIG, STDEVP, GROUPING, VAR, MAX, VARP (Read more here )

What is Use of @@ SPID in SQL Server?

A SPID is the returns sessions ID of the current user process. And using that session ID, we can find out that the last query was executed. (Read more here)

What is the Difference between Index Seek vs. Index Scan?

An index scan means that SQL Server reads all the rows in a table, and then returns only those rows that satisfy the search criteria. When an index scan is performed, all the rows in the leaf level of the index are scanned. This essentially means that all the rows of the index are examined instead of the table directly. This is sometimes compared to a table scan, in which all the table data is read directly. However, there is usually little difference between an index scan and a table scan.
An index seek, on the other hand, means that the Query Optimizer relies entirely on the index leaf data to locate rows satisfying the query condition. An index seek will be most beneficial in cases where a small percentage of rows will be returned. An index seek will only affect the rows that satisfy a query condition and the pages that contain these qualifying rows; in terms of performance, this is highly beneficial when a table has a very large number of rows. (Read more here)

What is the Maximum Size per Database for SQL Server Express?

SQL Server Express supports a maximum size of 4 GB per database, which excludes all the log files. 4 GB is not a very large size; however, if the database is properly designed and the tables are properly arranged in a separate database, this limitation can be resolved to a certain extent.
(Read more here)

How do We Know if Any Query is Retrieving a Large Amount of Data or very little data?

In one way, it is quite easy to figure this out by just looking at the result set; however, this method cannot be relied upon every time as it is difficult to reach a conclusion when there are many columns and many rows.
It is easy to measure how much data is retrieved from server to client side. The SQL Server Management Studio has feature that can measure client statistics. (Read more here)

What is the Difference between GRANT and WITH GRANT while Giving Permissions to the User?

In case of only GRANT, the username cannot grant the same permission to other users. On the other hand, with the option WITH GRANT, the username will be able to give the permission after receiving requests from other users. (Read more here)

How to Create Primary Key with Specific Name while Creating a Table?

CREATE TABLE [dbo].[TestTable](

[ID] [int] IDENTITY(1,1)NOTNULL,

[FirstName] [varchar](100)NULL,

CONSTRAINT [PK_TestTable] PRIMARYKEYCLUSTERED

([ID] ASC))

GO

(Read more here)

What is T-SQL Script to Take Database Offline – Take Database Online?

-- Take the Database Offline

ALTER DATABASE [myDB] SET OFFLINE WITH

ROLLBACK IMMEDIATE

GO

-- Take the Database Online

ALTER DATABASE [myDB] SET ONLINE

GO

(Read more here)

How to Enable/Disable Indexes?

--Disable Index

ALTER INDEX [IndexName] ON TableName DISABLE

GO

--Enable Index

ALTER INDEX [IndexName] ON TableName REBUILD

GO

(Read more here)

Can we Insert Data if Clustered Index is Disabled?

No, we cannot insert data if Clustered Index is disabled because Clustered Indexes are in fact original tables which are physically ordered according to one or more keys (Columns). (Read more here)

How to Recompile Stored Procedure at Run Time?

We can Recompile Stored Procedure in two ways.
Option 1:

CREATE PROCEDURE dbo.PersonAge(@MinAge INT, @MaxAge INT)

WITH RECOMPILE

AS

SELECT*

FROM dbo.tblPerson

WHERE Age <= @MinAge AND Age >= @MaxAge

GO

Option 2:
EXEC dbo.PersonAge65, 70 WITHRECOMPILE
We can use RECOMPILE hint with a query and recompile only that particular query. However, if the parameters are used in many statements in the stored procedure and we want to recompile all the statements, then instead of using the RECOMPILE option with all the queries, we have one better option that uses WITH RECOMPILE during stored procedure creation or execution.
This method is not recommended for large stored procedures because the recompilation of so many statements may outweigh the benefit of a better execution plan. (Read more here)

Is there any Performance Difference between IF EXISTS (Select null from table) and IF EXISTS (Select 1 from table)?

There is no performance difference between IF EXISTS (Select null from table) and IF EXISTS (Select 1 from table). (Read more here)

What is Difference in Performance between INSERT TOP (N) INTO Table and Using Top with INSERT?

INSERT TOP (N) INTO Table is faster than Using Top with INSERT but when we use INSERT TOP (N) INTO Table, the ORDER BY clause is totally ignored. (Read more here)

Does the Order of Columns in UPDATE statements Matter?

No, the order of columns in UPDATE statement does not matter for results updated.
Both the below options produce the same results.
Option 1:

UPDATE TableName

SET Col1 ='Value', Col2 ='Value2'

Option 2:

UPDATE TableName

SET Col2 ='Value2', Col1 ='Value'

What are Policy Management Terms?

To have a better grip on the concept of Policy-based management, there are some key terms you need to understand.
Target – A type of entity that is appropriately managed by Policy-based management. For example, a table, database and index, to name a few.
Facet -A property that can be managed in policy-based management. A clear example of facet is the name of Trigger or the Auto Shrink Property of database.
Conditions – Criteria that specifies the state of facet to true or false. For example, you can adjust the state of a facet that gives you clear specifications of all stored procedures in the Schema ‘Banking’.
Policy – A set of rules specified for the server objects or the properties of database.
(Read more here)

What is the ‘FILLFACTOR’?

A “FILLFACTOR” is one of the important arguments that can be used while creating an index.
According to MSDN, FILLFACTOR specifies a percentage that indicates how much the Database Engine should fill each index page during index creation or rebuild. Fill-factor is always an integer valued from 1 to 100. The fill-factor option is designed for improving index performance and data storage. By setting the fill-factor value, you specify the percentage of space on each page to be filled with data, reserving free space on each page for future table growth.
Specifying a fill-factor value of 70 would imply that 30 percent of each page will be left empty, providing space for index expansion as data is added to the underlying table. The fill-factor setting applies only when the index is created or rebuilt. (Read more here)

Where in MS SQL Server is ’100’ equal to ‘0’?

Fill-factor settings of 0 and 100 are equal! (Read more here)

What are Points to Remember while Using the FILLFACTOR Argument?

If fill-factor is set to 100 or 0, the Database Engine fills pages to their capacity while creating indexes.
The server-wide default FILLFACTOR is set to 0.
To modify the server-wide default value, use the sp_configure system stored procedure.
To view the fill-factor value of one or more indexes, use sys.indexes.
To modify or set the fill-factor value for individual indexes, use CREATE INDEX or ALTER INDEX statements.
Creating a clustered index with a FILLFACTOR < 100 may significantly increase the amount of space the data occupies because the Database Engine physically reallocates the data while building the clustered index. (Read more here)

What is a ROLLUP Clause?

ROLLUP clause is used to do aggregate operation on multiple levels in hierarchy. If we want sum on different levels without adding any new column, then we can do it easily using ROLLUP. We have to just add the WITH ROLLUP Clause in group by clause. (Read more here)

What are Various Limitations of the Views?

ORDER BY clause does not work in View.

(Read more here)

Regular queries or Stored Procedures give us flexibility when we need another column; we can add a column to regular queries right away. If we want to do the same with Views, then we will have to modify them first.

(Read more here)

Index created on view not used often.

(Read more here)

Once the view is created and if the basic table has any column added or removed, it is not usually reflected in the view till it is refreshed.

(Read more here)

One of the most prominent limitations of the View it is that it does not support COUNT (*); however, it can support COUNT_BIG (*).

(Read more here)

UNION Operation is now allowed in Indexed View.

(Read More Here)

We cannot create an Index on a nested View situation means we cannot create index on a view which is built from another view.

(Read More Here)

SELF JOIN Not Allowed in Indexed View.

(Read more here)

Outer Join Not Allowed in Indexed Views.

(Read more here)

Cross Database Queries Not Allowed in Indexed View.

(Read more here)

What is a Covered index?

It is an index that can satisfy a query just by its index keys without having needed to touch the data pages.
It means that when a query is fired, SQL Server doesn’t need to go to the table to retrieve the rows, but can produce the results directly from the index as the index covers all the columns used in query. (Read more here)

When I Delete any Data from a Table, does the SQL Server reduce the size of that table?

When data are deleted from any table, the SQL Server does not reduce the size of the table right away; however, it marks those pages as free pages, showing that they belong to the table. When new data are inserted, they are put into those pages first. Once those pages are filled up, SQL Server will allocate new pages. If you wait for sometime, the background process de-allocates the pages, finally reducing the page size. (Read more here)

What are Wait Types?

There are three types of wait types, namely,
Resource Waits. Resource waits occur when a worker requests access to a resource that is not available because that resource is either currently used by another worker or it’s not yet available.
Queue Waits. Queue waits occur when a worker is idle, waiting for work to be assigned.
External Waits. External waits occur when an SQL Server worker is waiting for an external event. (Read more here)

How to Stop Log File Growing too Big?

If your Transaction Log file was growing too big and you wanted to manage its size, then instead of truncating transaction log file, you should choose one of the options mentioned below.
1) Convert the Recovery Model to Simple Recovery

If you change your recovery model to Simple Recovery Model, then you will not encounter the extraordinary growth of your log file. However, please note if you have one long running transaction it will for sure grow your log file till the transaction is complete.

2) Start Taking Transaction Log Backup

In this Full Recovery Model, your transaction log will grow until you take a backup of it. You need to take the T-Log Backup at a regular interval. This way, your log would not grow beyond some limits.

(Read more here)

If any Stored Procedure is Encrypted, then can we see its definition in Activity Monitor?

No, we can’t see definition of encrypted stored procedure in Activity Monitor.

How to Copy Data from One Table to Another Table?

There are multiple ways to do this.
1) INSERT INTO SELECT
This method is used when table is already created in the database earlier and data have to be inserted into this table from another table. If columns listed in the INSERT clause and SELECT clause are same, listing them is not required.
2) SELECT INTO
This method is used when table is not created earlier and it needs to be created when data from one table must be inserted into a newly created table from another table. The new table is created using the same data types as those in selected columns. (Read more here)

What is Catalog Views?

Catalog views return information that is used by the SQL Server Database Engine. Catalog Views are the most general interface to the catalog metadata and provide the most efficient way to obtain, transform, and present customized forms of this information. All user-available catalog metadata is exposed through catalog views.

What is PIVOT and UNPIVOT?

A Pivot Table can automatically sort, count, and total the data stored in one table or spreadsheet and create a second table displaying the summarized data. The PIVOT operator turns the values of a specified column into column names, effectively rotating a table.
In simpler word UNPIVOT table is reverse of PIVOT Table, however it is not exactly true. UNPIVOTING is for sure reverse operation to PIVOTING but if during PIVOTING process data aggregated the UNPIVOT table does not return to original table. (Read more here)

What is a Filestream?

Filestream allows you to store large objects in the file system and have these files integrated within the database. It enables SQL Server-based applications to store unstructured data such as documents, images, audios and videos in the file system. FILESTREAM basically integrates the SQL Server Database Engine with New Technology File System (NTFS); it basically stores the data in varbinary (max) data type. Using this data type, the unstructured data is stored in the NTFS file system, and the SQL Server Database Engine manages the link between the Filestream column and the actual file located in the NTFS. Using Transact-SQL statements users can insert, update, delete and select the data stored in FILESTREAM-enabled tables.

What is SQLCMD?

sqlcmd is enhanced version of the isql and osql, and it provides way more functionality than other two options. In other words, sqlcmd is better replacement of isql (which will be deprecated eventually) and osql (not included in SQL Server 2005 RTM). sqlcmd can work in two modes – i) BATCH and ii) interactive modes. (Read more here)

What do you mean by TABLESAMPLE?

TABLESAMPLE allows you to extract a sampling of rows from a table in the FROM clause. The rows retrieved are random and they are not in any order. This sampling can be based on a percentage of number of rows. You can use TABLESAMPLE when only a sampling of rows is necessary for the application instead of a full result set. (Read more here)

What is ROW_NUMBER()?

ROW_NUMBER() returns a column as an expression that contains the row’s number within the result set. This is only a number used in the context of the result set; if the result changes, the ROW_NUMBER() will change.

What are Ranking Functions?

Ranking functions return a ranking value for each row in a partition. All the ranking functions are non-deterministic. The different Ranking functions are as follows:
ROW_NUMBER () OVER ([<partition_by_clause>] <order_by_clause>)
Returns the sequential number of a row within a partition of a result set, starting at 1 for the first row in each partition.
RANK () OVER ([<partition_by_clause>] <order_by_clause>)
Returns the rank of each row within the partition of a result set.
DENSE_RANK () OVER ([<partition_by_clause>] <order_by_clause>)
Returns the rank of rows within the partition of a result set, without any gaps in the ranking. (Read more here )

What is Change Data Capture (CDC) in SQL Server 2008?

Change Data Capture (CDC) records INSERTs, UPDATEs, and DELETEs applied to SQL Server tables and makes a record available of what changed, where, and when, in simple relational ‘change tables’ rather than in an esoteric chopped salad of XML. These change tables contain columns that reflect the column structure of the source table you have chosen to track along with the metadata needed to understand the changes that have been made.

How will you Handle Error in SQL SERVER 2008?

SQL Server now supports the use of TRY…CATCH constructs for providing rich error handling. TRY…CATCH lets us build error handling at the level we need, in the way we need to by setting a region where if any error occurs, it will break out of the region and head to an error handler. The basic structure is as follows:

BEGIN TRY
<code>
END TRY
BEGIN CATCH
<code>
END CATCH

So if any error occurs in the TRY block, then execution is diverted to the CATCH block, and the error can be resolved.

What is RAISEERROR?

RaiseError generates an error message and initiates error processing for the session. RAISERROR can either reference a user-defined message stored in the sys.messages catalog view or build a message dynamically. The message is returned as a server error message to the calling application or to an associated CATCH block of a TRY…CATCH construct. (Read more here)

How to Rebuild the Master Database?

Master database is system database and it contains information about running server’s configuration. When SQL Server 2005 is installed, it usually creates master, model, msdb, tempdb, resourcedb and the distribution system database by default. Only the Master database is the one which is absolutely a must-have database. Without the Master database, the SQL Server cannot be started. This is the reason why it is extremely important to backup the Master database.
To rebuild the Master database, run Setup.exe, verify, and repair a SQL Server instance, and rebuild the system databases. This procedure is most often used to rebuild the master database for a corrupted installation of SQL Server. (Read more here)

What is the XML Datatype?

The xml data type lets you store XML documents and fragments in a SQL Server database. An XML fragment is an XML instance that has a missing single top-level element. You can create columns and variables of the xml type and store XML instances in them. The xml data type and associated methods help integrate XML into the relational framework of SQL Server.

What is Data Compression?

In SQL SERVE 2008, Data Compression comes in two flavors:

Row Compression
Page Compression

Row Compression

Row compression changes the format of physical storage of data. It minimize the metadata (column information, length, offsets etc) associated with each record. Numeric data types and fixed-length strings are stored in variable-length storage format, just like Varchar. (Read more here)

Page Compression

Page compression allows common data to be shared between rows for a given page. It uses the following techniques to compress data:

Row compression.
Prefix Compression. For every column in a page, duplicate prefixes are identified. These prefixes are saved in compression information headers which resides after the page header. A reference number is assigned to these prefixes and that reference number is replaced where ever those prefixes are being used.

Dictionary Compression

Dictionary compression searches for duplicate values throughout the page and stores them in CI. The main difference between prefix and dictionary compression is that the former is only restricted to one column while the latter is applicable to the complete page.

What is Use of DBCC Commands?

The Transact-SQL programming language provides DBCC statements that act as Database Console Commands for SQL Server. DBCC commands are used to perform the following tasks.

Maintenance tasks on database, index, or filegroup.
Tasks that gather and display various types of information.
Validation operations on a database, table, index, catalog, filegroup, or allocation of database pages.
Miscellaneous tasks such as enabling trace flags or removing a DLL from memory. (Read more here)

How to Copy the Tables, Schema and Views from one SQL Server to Another?

There are multiple ways to do this.

“Detach Database” from one server and “Attach Database” to another server.
Manually script all the objects using SSMS and run the script on a new server.
Use Wizard of SSMS. (Read more here)

How to Find Tables without Indexes?

Run the following query in the Query Editor.

USE <database_name>;

GO

SELECT SCHEMA_NAME(schema_id) AS schema_name

,name AS table_name

FROM sys.tables

WHERE OBJECTPROPERTY(OBJECT_ID,'IsIndexed') = 0

ORDER BY schema_name, table_name;

GO

What are the Advantages of Using CTE?

Using CTE improves the readability and enables easy maintenance of complex queries.
The query can be divided into separate, simple, and logical building blocks, which can be then used to build more complex CTEs until the final result set is generated.
CTE can be defined in functions, stored procedures, triggers or even views.
After a CTE is defined, it can be used as a Table or a View and can SELECT, INSERT, UPDATE or DELETE Data.

How can we Rewrite Sub-Queries into Simple Select Statements or with Joins?

Yes. We can rewrite sub-queries using the Common Table Expression (CTE). A Common Table Expression (CTE) is an expression that can be thought of as a temporary result set which is defined within the execution of a single SQL statement. A CTE is similar to a derived table in that it is not stored as an object and lasts only for the duration of the query.
e.g.



USE AdventureWorks

GO

WITH EmployeeDepartment_CTE AS (

SELECT EmployeeID,DepartmentID,ShiftID

FROM HumanResources.EmployeeDepartmentHistory

)

SELECT ecte.EmployeeId,ed.DepartmentID, ed.Name,ecte.ShiftID

FROM HumanResources.Department ed

INNER JOIN EmployeeDepartment_CTE ecte ON ecte.DepartmentID = ed.DepartmentID

GO

What is CLR?

In SQL Server 2008, SQL Server objects such as user-defined functions can be created using such CLR languages. This CLR language support extends not only to user-defined functions, but also to stored procedures and triggers. You can develop such CLR add-ons to SQL Server using Visual Studio 2008. (Read more here)

What are Synonyms?

Synonyms give you the ability to provide alternate names for database objects. You can alias object names; for example, using the Employee table as Emp. You can also shorten names. This is especially useful when dealing with three and four part names; for example, shortening server.database.owner.object to object. (Read more here)

What is LINQ?

Language Integrated Query (LINQ) adds the ability to query objects using .NET languages. The LINQ to SQL object/relational mapping (O/RM) framework provides the following basic features:

Tools to create classes (usually called entities) mapped to database tables
Compatibility with LINQ’s standard query operations
The DataContext class with features such as entity record monitoring, automatic SQL statement generation, record concurrency detection, and much more

What are Isolation Levels?

Transactions specify an isolation level that defines the degree to which one transaction must be isolated from resource or data modifications made by other transactions. Isolation levels are described in terms of which concurrency side-effects, such as dirty reads or phantom reads, are allowed.
Transaction isolation levels control the following:

Whether locks are taken when data is read, and what type of locks are requested.
How long the read locks are held.
Whether a read operation referencing rows modified by another transaction
- blocks until the exclusive lock on the row is freed,
- retrieves the committed version of the row that existed at the time the statement or transaction started, and
- reads the uncommitted data modification.(Read more here)

What is Use of EXCEPT Clause?

EXCEPT clause is similar to MINUS operation in Oracle. The EXCEPT query and MINUS query return all rows in the first query that are not returned in the second query. Each SQL statement within the EXCEPT query and MINUS query must have the same number of fields in the result sets with similar data types. (Read more here)

What is XPath?

XPath uses a set of expressions to select nodes to be processed. The most common expression that you’ll use is the location path expression, which returns back a set of nodes called a node set. XPath can use both an unabbreviated and abbreviated syntax. The following is the unabbreviated syntax for a location path:
/axisName::nodeTest[predicate]/axisName::nodeTest[predicate]

What is NOLOCK?

Using the NOLOCK query optimizer hint is generally considered a good practice in order to improve concurrency on a busy system. When the NOLOCK hint is included in a SELECT statement, no locks are taken on data when data is read. The result is a Dirty Read, which means that another process could be updating the data at the exact time you are reading it. There are no guarantees that your query will retrieve the most recent data. The advantage to performance is that your reading of data will not block updates from taking place, and updates will not block your reading of data. SELECT statements take Shared (Read) locks. This means that multiple SELECT statements are allowed simultaneous access, but other processes are blocked from modifying the data. The updates will queue until all the reads have completed, and reads requested after the update will wait for the updates to complete. The result to your system is delay (blocking). (Read more here)

What is the Difference between Update Lock and Exclusive Lock?

When Exclusive Lock is on any process, no other lock can be placed on that row or table. Every other process have to wait till Exclusive Lock completes its tasks.
Update Lock is a type of Exclusive Lock, except that it can be placed on the row which already has Shared Lock on it. Update Lock reads the data of the row which has the Shared Lock as soon as the Update Lock is ready to change the data it converts itself to the Exclusive Lock.

What are the basic functions for master, msdb, model, tempdb and resource databases?

The master database holds information for all the databases located on the SQL Server instance, and it is the glue that holds the engine together. Because SQL Server cannot start without a functioning master database, you must administer this database with care.
The msdb database stores information regarding database backups, SQL Agent information, DTS packages, SQL Server jobs, and some replication information such as for log shipping.
The tempdb holds temporary objects such as global and local temporary tables and stored procedures.
The model is essentially a template database used in the creation of any new user database created in the instance.
The resource Database is a read-only database that contains all the system objects that are included in the SQL Server. SQL Server system objects such as sys.objects are physically persisted in the Resource database, but they logically appear in the sys schema of every database. The Resource database does not contain user data or user metadata.

What is the Maximum Number of Index per Table?

For SQL Server 2005:
1 Clustered Index + 249 Nonclustered Index = 250 Index.
For SQL Server 2008:
1 Clustered Index + 999 Nonclustered Index = 1000 Index. (Read more here)

Explain Few of the New Features of SQL Server 2008 Management Studio

SQL Server 2008 Microsoft has upgraded SSMS with many new features as well as added tons of new functionalities requested by DBAs for long time.
A few of the important new features are as follows:

IntelliSense for Query Editing
Multi Server Query
Query Editor Regions
Object Explorer Enhancements
Activity Monitors

Explain IntelliSense for Query Editing:

After implementing IntelliSense, we will not have to remember all the syntax or browse online references. IntelliSense offers a few additional features besides just completing the keyword.

Explain MultiServer Query:

SSMS 2008 has a feature to run a query on different servers from one query editor window. First of all, make sure that you registered all the servers under your registered server. Once they are registered, right click on server group name and click New Query.
e.g. for server version information,

SELECT

SERVERPROPERTY('Edition') AS Edition,

SERVERPROPERTY('ProductLevel') AS ProductLevel,

SERVERPROPERTY('ProductVersion') AS ProductVersion

Explain Query Editor Regions:

When the T-SQL code is more than hundreds of lines, after a while, it becomes more and more confusing.
The regions are defined by the following hierarchy:
From first GO command to the next GO command.
Statements between BEGIN – END, BEGIN TRY – END TRY, BEGIN CATCH – END CATCH

Explain Object Explorer Enhancements:

In Object Explorer Detail, the new feature is Object Search. Enter any object name in the object search box and the searched result will be displayed in the same window as Object Explorer Detail.
Additionally, there are new wizards which help you perform several tasks, from policy management to disk monitoring. One cool thing is that everything displayed in the object explorer details screen can be right away copied and pasted to Excel without any formatting issue.

Explain Activity Monitors:

There are four graphs

percent; Processor Time,
Waiting Tasks,
Database I/O,
Batch Requests/Sec

All the four tabs provide very important information; however, the one which I refer most is “Recent Expensive Queries.” Whenever I find my server running slow or having any performance-related issues, my first reaction is to open this tab and see which query is running slow. I usually look at the query with the highest number for Average Duration. The Recent Expensive Queries monitors only show queries which are in the SQL Server cache at that moment.

1.What is SQL Azure?
SQL Azure is a cloud based relational database as a Service offered by Microsoft. Conceptually it is SQL server in the cloud.

2.What is cloud computing?
National Institute of standards and computing definition of cloud computing:
Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.
[TIP: Remember Key words On Demand, Scalable, Self-service, and Measurable. Now take the first word from each key word which gives us OSSM which can be pronounced as Awesome. Thus remember cloud computing is Awesome! Tip courtesy: Dave Nielsen]

3.How is SQL Azure different than SQL server?
SQL Azure is a cloud based service and so it has own set of pros and cons when compared to SQL server. SQL Azure service benefits includes on demand provisioning, high availability, reduced management overhead and scalability. But SQL Azure abstracts some details from the subscriber which can be good or bad which depends on the context of the need.

4.How many replicas are maintained for each SQL Azure database?
For each database, three replicas are maintained for each database that one provisions. One of them is primary replica. All read/write happen on primary replica and other replicas are kept in sync with primary replica. If for some reason, primary goes down, other replica is promoted to primary. All this happens under the hood.

5.How can we migrate from SQL server to SQL Azure?
For Data Migration, we can use BCP or SSIS. And for schema Migration we can use Generate Script Wizard. Also, we could use a Tool called SQL Azure migration wizard available on codeplex.

6.Which tools are available to manage SQL Azure databases and servers?
We can manage SQL Azure database using SQL server management server 2008 R2. Also, we can manage SQL Azure databases and servers through a Silverlight app integrated in Azure management portal.

7.Tell me something about security and SQL Azure.
SQL Azure service allows blocking a request based on its IP address through SQL Azure firewall. It uses SQL server Authentication mechanism to authenticate connections. Also connections to SQL Azure are SSL-encrypted by default.

8.What is SQL Azure Firewall?
SQL Azure firewall is a security mechanism that blocks requests based on its IP address.

9.What is the difference between web edition and business edition?
SQL Azure Web edition database Max Size is 5 GB whereas the business edition supports Max Size up to 50 GB. The size of a web edition database can be increased (/decreased) in the increments (/decrements) of 1 GB whereas the size of a business edition can be increased in the increments of 10 GB.

10.How do we synchronize On Premise SQL server with SQL Azure?
We could use a No code solution called DATA SYNC (currently in community technology preview) to synchronize on-premise SQL server with SQL Azure. We can also develop custom solutions using SYNC framework.

11.How do we Backup SQL Azure Data?
SQL Azure keeps three replicas of a database to tackle hardware level issues. To tackle user level errors, we can use COPY command that allows us to create a replica of a SQL Azure database. We can also backup SQL Azure data to local SQL server using BCP, SSIS, etc. but as of now, point in time recovery is not supported.

12.What is the current pricing model of SQL Azure?
Charges for SQL Azure consumption is based on 1) Size 2) Data Transfer.
[For contemporary pricing model, read: http://www.microsoft.com/windowsazure/pricing/ ]

13.What is the current limitation of the size of SQL Azure DB?
Maximum size of a SQL Azure database is 50 GB.

14.How do you handle datasets larger than 50 GB?
As of now, we have to build custom solution at application level that can handle scale out of underlying SQL Azure databases. But Microsoft has announced, SQL Azure Federations that will assist scaling out of SQL Azure databases. And scale out means that we are splitting the data into smaller subsets spread across multiple databases.

15.What happens when the SQL Azure database reaches Max Size?
Read operations continue to work but create/insert/update operations are throttled. You can drop/delete/truncate data.

16.How many databases can we create in a single server?
150 databases (including master database) can be created in a single SQL Azure server.

17.How many servers can we create in a single subscription?
As of now, we can create six servers under a single subscription.

18.How do you improve the performance of a SQL Azure Database?
We can tune a SQL Azure database using information available from execution plan and statistics of a query. We could use SQL Azure’s Dynamic Management views to monitor and manage SQL Azure database.
Also, SQL Azure performance is affected by network latency and bandwidth. Considering this, code near application topology gives the best performance.

19.What is code near application topology?
Code near application topology means that the SQL Azure database and the windows azure hosted service consuming the data are hosted in the same Azure datacenter.
[FYI: in the code far application topology, the app connects to SQL Azure from outside the Microsoft data center]

20.What were the latest updates to SQL Azure service?
Latest SQL Azure updates include multiple servers per subscription, SQL Azure co administrator support, creating Firewall rules for servers with IP detect.
[A constantly updated list of SQL Azure features is available at http://beyondrelational.com/whatisnew/sqlserver/azure.aspx]

21.When does a workload on SQL Azure get throttled?
When database reaches its maximum size update/insert/create operations get throttled. Also there are policies in place that does not allow to a workload to exploit a shared physical server. In other words, the policies make sure that all workload get a fair share of shared physical server. Now, a workload can get soft throttled that means that the workload has crossed the safety threshold. A workload can also got hard throttled which means that a SQL Azure machine is out of resources and it does not accept new connections. We can know more about what happened by decoding reason codes.
These were SQL Azure specific interview questions but remember that SQL server specific interview questions that we have seen so far can also appear in SQL Azure context since SQL Azure is “SQL server in the cloud”. Also questions specific to supported/unsupported features can be asked. I have not included the questions specific to unsupported features because it keeps on changing. Read general guidelines and limitations. Also note that SQL Azure is evolving very fast and it is important to keep a tab on the features that are added in service releases.

4 comments:

UnknownJuly 15, 2013 at 11:26 PM

protected void Page_Load(object sender, EventArgs e)
{
if (Page.IsPostBack == false)
{
DirectoryInfo RootDir = new DirectoryInfo(Server.MapPath("~/"));
TreeNode RootNode = OutPutDirectory(RootDir, null);
TreeView1.Nodes.Add(RootNode);
}
}

TreeNode OutPutDirectory(DirectoryInfo directory, TreeNode parentNode)
{
if (directory == null) return null;
TreeNode DirNode = new TreeNode(directory.Name);
DirectoryInfo[] subDir = directory.GetDirectories();
for (int DirCount = 0; DirCount < subDir.Length; DirCount++)
{
OutPutDirectory(subDir[DirCount], DirNode);
}
FileInfo[] file = directory.GetFiles();
for (int fcount = 0; fcount < file.Length; fcount ++)
{
DirNode.ChildNodes.Add(new TreeNode(file[fcount].Name));
}
if (parentNode == null)
{
return DirNode;
}
else
{
parentNode.ChildNodes.Add(DirNode);
return parentNode;
}

}
UnknownJuly 15, 2013 at 11:33 PM
protected void grid_RowCommand(object sender, GridViewCommandEventArgs e)
{
try
{
if (e.CommandArgument == "Save")
{
TextBox name_txt = (TextBox)grid.FooterRow.FindControl("TextBox1");
TextBox Email_txt = (TextBox)grid.FooterRow.FindControl("TextBox2");
TextBox phone_txt = (TextBox)grid.FooterRow.FindControl("TextBox3");
TextBox Address_txt = (TextBox)grid.FooterRow.FindControl("TextBox4");
FileUpload upld = (FileUpload)grid.FooterRow.FindControl("FileUpload2");

string pathe="";
string spath="";
string fileName="";
if (upld.HasFile)//E:\wellpaper\waall
{
fileName = upld.FileName;
pathe = @"~\Image\" + fileName;
spath = Server.MapPath("Image");
spath = spath+=@"\"+upld.FileName;
upld.SaveAs(spath);

}
cmd.CommandText = "insert into graft(Name,Email,Phone,Address,Image) values ('" + name_txt.Text + "','" + Email_txt.Text + "','" + phone_txt.Text + "','" + Address_txt.Text + "','" + pathe + "')";
cmd.Connection = con;
con.Open();
cmd.ExecuteNonQuery();
con.Close();
show.Visible = true;
show.Text = "Data inserted successfully";
gridfill();
drp.DataBind();
name_txt.Text = "";
Email_txt.Text = "";
phone_txt.Text = "";
Address_txt.Text = "";
}

}
catch (Exception ex)
{
}
}

protected void grid_OnRowDeleting(object sender, GridViewDeleteEventArgs e)
{
try
{
int id = Convert.ToInt32(grid.DataKeys[e.RowIndex].Value.ToString());

cmd.CommandText = "delete from graft where id="+id+"";
cmd.Connection = con;
con.Open();
cmd.ExecuteNonQuery();
con.Close();
gridfill();
drp.DataBind();
show.Visible = true;
show.Text = "Data delete successfully";

}
catch (Exception ex)
{
}

}
protected void grid_DataBound(object sender, EventArgs e)
{

}
protected void grid_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow && e.Row.RowIndex==grid.EditIndex)
{
DropDownList drpName = e.Row.FindControl("drp") as DropDownList;
HiddenField Name = e.Row.FindControl("hh") as HiddenField;

if (Name.Value != null)
{
drpName.SelectedValue = Name.Value.ToString();
}
}
}
}
UnknownJuly 15, 2013 at 11:35 PM
protected void Button1_Click(object sender, EventArgs e)
{
try
{
string frommailid = "Mithlesh.kumar@Cenduit.com";
SmtpClient smtpClient = new SmtpClient();
MailMessage message = new MailMessage();
MailAddress fromAddress = new MailAddress("Mithlesh international <" + frommailid + ">");
// MailAddress ccAddress = new MailAddress("singhmukesh325@gmail.com");
MailAddress toAddress = new MailAddress(TextBox1.Text);
smtpClient.Host = "";
smtpClient.Credentials = new System.Net.NetworkCredential("", "");
smtpClient.Port = 25;
message.From = fromAddress;
message.To.Add(toAddress);
//message.CC.Add(ccAddress);
message.Subject = TextBox2.Text;
message.IsBodyHtml = true;
string strHTML;

message.Body = strHTML;
smtpClient.Send(message);
}
catch(Exception ex)
{
}
}
AnonymousNovember 11, 2013 at 6:15 PM
These are some very useful SQL Commands.

Truncate all tables:

EXEC sp_MSforeachtable 'TRUNCATE TABLE ?'
Delete data from all tables:

EXEC sp_MSForEachTable "DELETE FROM ?"
Disable all constraints from all tables:

EXEC sp_msforeachtable "ALTER TABLE ? NOCHECK CONSTRAINT all"
Enable all constraints from all tables:

EXEC sp_msforeachtable "ALTER TABLE ? WITH CHECK CHECK CONSTRAINT all"

Disable all triggers from all tables:

EXEC sp_msforeachtable "ALTER TABLE ? DISABLE TRIGGER all"
Enable all triggers from all tables:

EXEC sp_msforeachtable "ALTER TABLE ? ENABLE TRIGGER all"
Getting all column information of the table:

Select* fromINFORMATION_SCHEMA.COLUMNS
where table_name='Table Name'

Getting list of stored procedure modified in last N days:

SELECT name
FROMsys.objects
WHEREtype ='P'
ANDDATEDIFF(D,modify_date,GETDATE())< N

Note: Replace N with any number.

Getting a list of stored procedures created in the last N days:

SELECT name
FROMsys.objects
WHEREtype ='P'
ANDDATEDIFF(D,create_date,GETDATE())< N

Note: Replace N with any number.