MS SQL Server interview questions

This one always gets asked. For a while the database interview questions were limited to Oracle and generic database design questions. This is a set of more than a hundred Microsoft SQL Server interview questions. Some questions are open-ended, and some do not have answers.

  1. What is normalization? - Well a relational database is basically composed of tables that contain related data. So the Process of organizing this data into tables is actually referred to as normalization.
  2. What is a Stored Procedure? - Its nothing but a set of T-SQL statements combined to perform a single task of several tasks. Its basically like a Macro so when you invoke the Stored procedure, you actually run a set of statements.
  3. Can you give an example of Stored Procedure? - sp_helpdb , sp_who2, sp_renamedb are a set of system defined stored procedures. We can also have user defined stored procedures which can be called in similar way.
  4. What is a trigger? - Triggers are basically used to implement business rules. Triggers is also similar to stored procedures. The difference is that it can be activated when data is added or edited or deleted from a table in a database.
  5. What is a view? - If we have several tables in a db and we want to view only specific columns from specific tables we can go for views. It would also suffice the needs of security some times allowing specfic users to see only specific columns based on the permission that we can configure on the view. Views also reduce the effort that is required for writing queries to access specific columns every time.
  6. What is an Index? - When queries are run against a db, an index on that db basically helps in the way the data is sorted to process the query for faster and data retrievals are much faster when we have an index.
  7. What are the types of indexes available with SQL Server? - There are basically two types of indexes that we use with the SQL Server. Clustered and the Non-Clustered.
  8. What is the basic difference between clustered and a non-clustered index? - The difference is that, Clustered index is unique for any given table and we can have only one clustered index on a table. The leaf level of a clustered index is the actual data and the data is resorted in case of clustered index. Whereas in case of non-clustered index the leaf level is actually a pointer to the data in rows so we can have as many non-clustered indexes as we can on the db.
  9. What are cursors? - Well cursors help us to do an operation on a set of data that we retreive by commands such as Select columns from table. For example : If we have duplicate records in a table we can remove it by declaring a cursor which would check the records during retreival one by one and remove rows which have duplicate values.
  10. When do we use the UPDATE_STATISTICS command? - This command is basically used when we do a large processing of data. If we do a large amount of deletions any modification or Bulk Copy into the tables, we need to basically update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.
  11. Which TCP/IP port does SQL Server run on? - SQL Server runs on port 1433 but we can also change it for better security.
  12. From where can you change the default port? - From the Network Utility TCP/IP properties –> Port number.both on client and the server.
  13. Can you tell me the difference between DELETE & 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.
  14. Can we use Truncate command on a table which is referenced by FOREIGN KEY? - No. We cannot use Truncate command on a table with Foreign Key because of referential integrity.
  15. What is the use of DBCC commands? - DBCC stands for database consistency checker. We use these commands to check the consistency of the databases, i.e., maintenance, validation task and status checks.
  16. Can you give me some DBCC command options?(Database consistency check) - DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked.and DBCC CHECKALLOC - To check that all pages in a db are correctly allocated. DBCC SQLPERF - It gives report on current usage of transaction log in percentage. DBCC CHECKFILEGROUP - Checks all tables file group for any damage.
  17. What command do we use to rename a db? - sp_renamedb ‘oldname’ , ‘newname’
  18. Well sometimes sp_reanmedb may not work you know because if some one is using the db it will not accept this command so what do you think you can do in such cases? - In such cases we can first bring to db to single user using sp_dboptions and then we can rename that db and then we can rerun the sp_dboptions command to remove the single user mode.
  19. What is the difference between a HAVING CLAUSE and a WHERE CLAUSE? - Having Clause is basically used only with the GROUP BY function in a query. WHERE Clause is applied to each row before they are part of the GROUP BY function in a query.
  20. What do you mean by COLLATION? - Collation is basically the sort order. There are three types of sort order Dictionary case sensitive, Dictonary - case insensitive and Binary.
  21. What is a Join in SQL Server? - Join actually puts data from two or more tables into a single result set.
  22. Can you explain the types of Joins that we can have with Sql Server? - There are three types of joins: Inner Join, Outer Join, Cross Join
  23. When do you use SQL Profiler? - SQL Profiler utility allows us to basically track connections to the SQL Server and also determine activities such as which SQL Scripts are running, failed jobs etc..
  24. 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 dbs using T-SQL Statements.
  25. Can you link only other SQL Servers or any database servers such as Oracle? - We can link any server provided we have the OLE-DB provider from Microsoft to allow a link. For Oracle we have a OLE-DB provider for oracle that microsoft provides to add it as a linked server to the sql server group.
  26. Which stored procedure will you be running to add a linked server? - sp_addlinkedserver, sp_addlinkedsrvlogin
  27. What are the OS services that the SQL Server installation adds? - MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-ordinator)
  28. Can you explain the role of each service? - SQL SERVER - is for running the databases SQL AGENT - is for automation such as Jobs, DB Maintanance, Backups DTC - Is for linking and connecting to other SQL Servers
  29. How do you troubleshoot SQL Server if its running very slow? - First check the processor and memory usage to see that processor is not above 80% utilization and memory not above 40-45% utilization then check the disk utilization using Performance Monitor, Secondly, use SQL Profiler to check for the users and current SQL activities and jobs running which might be a problem. Third would be to run UPDATE_STATISTICS command to update the indexes
  30. Lets say due to N/W or Security issues client is not able to connect to server or vice versa. How do you troubleshoot? - First I will look to ensure that port settings are proper on server and client Network utility for connections. ODBC is properly configured at client end for connection ——Makepipe & readpipe are utilities to check for connection. Makepipe is run on Server and readpipe on client to check for any connection issues.
  31. What are the authentication modes in SQL Server? - Windows mode and mixed mode (SQL & Windows).
  32. Where do you think the users names and passwords will be stored in sql server? - They get stored in master db in the sysxlogins table.
  33. What is log shipping? Can we do logshipping with SQL Server 7.0 - Logshipping is a new feature of SQL Server 2000. We should have two SQL Server - Enterprise Editions. From Enterprise Manager we can configure the logshipping. In logshipping 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 we can use this as the DR (disaster recovery) plan.
  34. Let us say the SQL Server crashed and you are rebuilding the databases including the master database what procedure to you follow? - For restoring the master db we have to stop the SQL Server first and then from command line we can type SQLSERVER –m which will basically bring it into the maintenance mode after which we can restore the master db.
  35. Let us say master db itself has no backup. Now you have to rebuild the db so what kind of action do you take? - (I am not sure- but I think we have a command to do it).
  36. What is BCP? When do we use it? - BulkCopy is a tool used to copy huge amount of data from tables and views. But it won’t copy the structures of the same.
  37. What should we do to copy the tables, schema and views from one SQL Server to another? - We have to write some DTS packages for it.
  38. What are the different types of joins and what dies each do?
  39. What are the four main query statements?
  40. What is a sub-query? When would you use one?
  41. What is a NOLOCK?
  42. What are three SQL keywords used to change or set someone’s permissions?
  43. What is the difference between HAVING clause and the WHERE clause?
  44. What is referential integrity? What are the advantages of it?
  45. What is database normalization?
  46. Which command using Query Analyzer will give you the version of SQL server and operating system?
  47. Using query analyzer, name 3 ways you can get an accurate count of the number of records in a table?
  48. What is the purpose of using COLLATE in a query?
  49. What is a trigger?
  50. What is one of the first things you would do to increase performance of a query? For example, a boss tells you that “a query that ran yesterday took 30 seconds, but today it takes 6 minutes”
  51. What is an execution plan? When would you use it? How would you view the execution plan?
  52. What is the STUFF function and how does it differ from the REPLACE function?
  53. What does it mean to have quoted_identifier on? What are the implications of having it off?
  54. What are the different types of replication? How are they used?
  55. What is the difference between a local and a global variable?
  56. What is the difference between a Local temporary table and a Global temporary table? How is each one used?
  57. What are cursors? Name four types of cursors and when each one would be applied?
  58. What is the purpose of UPDATE STATISTICS?
  59. How do you use DBCC statements to monitor various aspects of a SQL server installation?
  60. How do you load large data to the SQL server database?
  61. How do you check the performance of a query and how do you optimize it?
  62. How do SQL server 2000 and XML linked? Can XML be used to access data?
  63. What is SQL server agent?
  64. What is referential integrity and how is it achieved?
  65. What is indexing?
  66. What is normalization and what are the different forms of normalizations?
  67. Difference between server.transfer and server.execute method?
  68. What id de-normalization and when do you do it?
  69. What is better - 2nd Normal form or 3rd normal form? Why?
  70. Can we rewrite subqueries into simple select statements or with joins? Example?
  71. What is a function? Give some example?
  72. What is a stored procedure?
  73. Difference between Function and Procedure-in general?
  74. Difference between Function and Stored Procedure?
  75. Can a stored procedure call another stored procedure. If yes what level and can it be controlled?
  76. Can a stored procedure call itself(recursive). If yes what level and can it be controlled.?
  77. How do you find the number of rows in a table?
  78. Difference between Cluster and Non-cluster index?
  79. What is a table called, if it does not have neither Cluster nor Non-cluster Index?
  80. Explain DBMS, RDBMS?
  81. Explain basic SQL queries with SELECT from where Order By, Group By-Having?
  82. Explain the basic concepts of SQL server architecture?
  83. Explain couple pf features of SQL server
  84. Scalability, Availability, Integration with internet, etc.)?
  85. Explain fundamentals of Data ware housing & OLAP?
  86. Explain the new features of SQL server 2000?
  87. How do we upgrade from SQL Server 6.5 to 7.0 and 7.0 to 2000?
  88. What is data integrity? Explain constraints?
  89. Explain some DBCC commands?
  90. Explain sp_configure commands, set commands?
  91. Explain what are db_options used for?
  92. What is the basic functions for master, msdb, tempdb databases?
  93. What is a job?
  94. What are tasks?
  95. What are primary keys and foreign keys?
  96. How would you Update the rows which are divisible by 10, given a set of numbers in column?
  97. If a stored procedure is taking a table data type, how it looks?
  98. How m-m relationships are implemented?
  99. How do you know which index a table is using?
  100. How will oyu test the stored procedure taking two parameters namely first name and last name returning full name?
  101. How do you find the error, how can you know the number of rows effected by last SQL statement?
  102. How can you get @@error and @@rowcount at the same time?
  103. What are sub-queries? Give example? In which case sub-queries are not feasible?
  104. What are the type of joins? When do we use Outer and Self joins?
  105. Which virtual table does a trigger use?
  106. How do you measure the performance of a stored procedure?
  107. Questions regarding Raiseerror?
  108. Questions on identity?
  109. If there is failure during updation of certain rows, what will be the state?
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237 Comments on MS SQL Server interview questions

  1. Hemachandra
    Posted 4/11/2007 at 4:39 am | Permalink

    What Is the Difference b/w Sql server7.0 & sql server2000

    A: Index view in add in sql 2000.
    1)we can add a index to the view by checking bind to schema

  2. Hemachandra
    Posted 4/12/2007 at 5:25 am | Permalink

    Ans for 5th heighest salary

    Select * From Employee E1 Where
    (N-1) = (Select Count(Distinct(E2.Salary)) From Employee E2 Where
    E2.Salary > E1.Salary)

  3. Zubair
    Posted 4/18/2007 at 11:37 am | Permalink

    I have one Employee table with EmpNo,name,Salary field
    i want list No of emloyee no who salary 5000, whos salary greater than 10,000 like as

    Answer:

    Select Count(*) as [Total Numbers], ‘500′ from Temployee where Salary

  4. Zubair
    Posted 4/18/2007 at 11:39 am | Permalink

    Select Count(*) as [Total Numbers], ‘500′ from Temployee where Salary

  5. Zubair
    Posted 4/18/2007 at 11:39 am | Permalink

    Union all
    Select Count(*) as [Total Numbers], ‘10000′ from Temployee where Salary between 500 and 1000

  6. Vishwanath Krishna
    Posted 4/23/2007 at 1:32 am | Permalink

    Answer - for this question:
    satpal Dhillon said,
    How can we get the top 10 rows of a table say’ emp’ out of total 50 rows?
    please sent me the answer if you have /

    SELECT TOP 10 * FROM sales
    WHERE stor_ID IN(SELECT TOP 50 stor_ID FROM sales ORDER BY QTY)

    Thanks
    Vishwa

  7. Arin
    Posted 5/12/2007 at 1:14 pm | Permalink

    Hi Guys,
    This is Arin you can get the fifth or nth highest salary of Employee table by using this statement.
    Thanks

    Select Min(Salary)
    From Employee
    Where Salary In
    (
    Select Top(5) Salary
    From Employee
    Order By Salary DESC
    )

  8. MKB
    Posted 5/17/2007 at 4:40 am | Permalink

    the query to find the top 2nd highest salary is below:

    select top 1* from Employee where Salary not in
    (select max(Salary) from Employee) order by Salary desc

  9. Alok
    Posted 5/17/2007 at 11:26 pm | Permalink

    People who find difficulty in getting the SECOND LARGEST SALARY from EMPLOYEE table—> Here is is the simplest query—>

    1)To get the total record of the employee with second larget salary:-

    select * from employee where salary=(select max(salary) from employee where salary

  10. Bibek
    Posted 5/22/2007 at 12:13 am | Permalink

    Normalization is a technique of database design that suggests that certain criteria be used when constructing a table layout (deciding what columns each table will have, and creating the key structure), where the idea is to eliminate redundancy of non-key data across tables. Normalization is usually referred to in terms of forms, and I will introduce only the first three, even though it is somewhat common to use other, more advanced forms (fourth, fifth, Boyce-Codd; see documentation).

  11. VISHRUTH
    Posted 6/9/2007 at 5:00 am | Permalink

    to get 4th max salary the coding is:

    select max(salary) from emp where salary notin(select top(4-1)salary from emp order by salary desc;

    to get any nth max salary the coding is:
    select max(salary) from emp where salary notin(select top(n-1)salary from emp order by salary desc;

    I think this wil help…….
    Cheers Mate!

  12. SreejuSN
    Posted 6/12/2007 at 5:28 am | Permalink

    SELECT MAX(Salary)
    FROM Employees
    WHERE Salary LESS THAN
    (SELECT MAX(SALARY) FROM Employees)

  13. Vishal
    Posted 6/13/2007 at 4:14 am | Permalink

    To delete duplicate data depend on specific column
    ————————————————–
    delete from tablename where columnname in (
    select max(column_name) from tablename group by columnname having count(column_name)>1)

    Thanks
    Vishal
    9849426400

  14. Nth Highest Salary Query
    Posted 6/19/2007 at 12:41 am | Permalink

    Select * From [Table] [T1] Where
    (2 = (Select Count(Distinct [ESalary]) From [Table] [T2] where [T1].[ESalary]

  15. Jeyaraj
    Posted 6/22/2007 at 9:53 am | Permalink

    SELECT COUNTRY, MINIMUM = MIN(PUB_ID),MAXIMUM = MAX(PUB_ID) FROM PUBLISHERS GROUP BY COUNTRY
    HAVING MAX(PUB_ID) >=’9000′ ORDER BY COUNT(COUNTRY) DESC COMPUTE COUNT(MAX(PUB_ID))

  16. Jeyaraj
    Posted 6/22/2007 at 9:54 am | Permalink

    WE CAN USE GROUP BY , HAVING CLAUSES , ORDER BY & COMPUTE BY IN A SAME SELECT STATEMENTS WHICH I HAD GIVE ABOVE

  17. Hitesh
    Posted 7/26/2007 at 1:08 am | Permalink

    To Find second Highest salary we can use this type of query
    –hitesh.shingade@gmail.com
    =============================================================
    CREATE PROC nth
    (
    @table_name sysname,
    @column_name sysname,
    @nth int
    )
    AS
    BEGIN

    SET @table_name = RTRIM(@table_name)
    SET @column_name = RTRIM(@column_name)

    DECLARE @exec_str CHAR(400)
    IF (SELECT OBJECT_ID(@table_name,’U')) IS NULL
    BEGIN
    RAISERROR(’Invalid table name’,18,1)
    RETURN -1
    END

    IF NOT EXISTS(SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = @table_name AND COLUMN_NAME = @column_name)
    BEGIN
    RAISERROR(’Invalid column name’,18,1)
    RETURN -1
    END

    IF @nth

  18. saravana
    Posted 7/31/2007 at 3:21 am | Permalink

    select max(salary) from tablename where salary>select max(salary) from tablename

  19. Tmoney
    Posted 7/31/2007 at 7:15 pm | Permalink

    rb said,
    hi vinay
    to get the table names from a database
    SELECT TABLE_NAME from information_schema.tables

    SELECT TABLE_NAME from information_schema.tables WHERE Table_Type = ‘BASE TABLE’
    OR
    SELECT [Name] AS TABLE_NAME FROM sysobjects WHERE xtype = ‘U’

  20. kishore dheram
    Posted 8/21/2007 at 7:38 am | Permalink

    This is query for 2nd highest salary in emp table.

    select max(sal) from emp where sal(select max(sal) from emp);

  21. Fazil
    Posted 9/5/2007 at 12:31 am | Permalink

    how to delete duplicate rows in table having rowid
    consider the table employe table with rowid,name and email .
    query look like this
    delete from tblemploye where rowid not in( select max(rowid) from tblemploye groupby name, email having count(*)>0)
    hope this helps!
    feel free to contact me if u have any queries

  22. fazil
    Posted 9/5/2007 at 12:51 am | Permalink

    delect identical rows from the table having rowid
    consider the customer table with rowid, name ,email

    delete from customer where rowid not in (select max(rowid) from customer group by name ,email having count(*)>1 )

    hope this helps

    For finding second largest salary

    select max(sal) from emp where sal not in (select distinct top 2 sal from emp order by emp desc)

  23. Ravi
    Posted 11/15/2007 at 2:24 am | Permalink

    Hi Please clear my doubt , When ever we use left outer join for two table of 4 rows and 3 rows , how many rows we get Assume : left is of 4 rows , How many rows if get while right outer join and full outer join .

    Please clarify this

  24. POORNIMA
    Posted 12/18/2007 at 6:33 am | Permalink

    RIGHT OUTER JOIN, indicates all rows in the second table are to be included in the results, regardless of whether there is matching data in the first table.Therefore 3 rows would be shown.

    In same way LEFT OUTER JOIN indicates the first table has to be included,so 4 rows would be there in results and the column in the second table for which there is no data is displayed as NULL

    To retain the nonmatching information by including nonmatching rows in the results of a join, use a full outer join. FULL OUTER JOIN, which includes all rows from both tables, regardless of whether or not the other table has a matching value.Therefore if columns have matching rows or not,all are selected..

    NOTE : FULL OUTER JOIN- the number of rows in results depend on the column which u have selected for comparing,assumind that both tabel have a similar column..the output would be of 5 rows,i.e 3 rows which are matching & 1 which is of first table which does not have data for specified column used for comparing.
    If both tables does not have any matching column then output would be
    FULL OUTER JOIN- 4 rows + 3 rows=7 rows

    HOPE IT HELPED U

  25. Niharika
    Posted 12/28/2007 at 7:20 am | Permalink

    use the following query to find all tables in a database

    “Select * from sysobjects where xtype = ‘u’”

  26. Simon
    Posted 1/17/2008 at 11:12 pm | Permalink

    Q-12: Additionally, DELETE is a logged operation, whereas TRUNCATE is a non-logged operation. Helpful to know when log space is limited.

  27. satyendra kumar
    Posted 1/23/2008 at 6:09 am | Permalink

    —To find out the 10 rows out of 50 rows in a table –
    select top 10 * from tname

    —to find out the second ( nth ) greatest salary from table —
    columnname = salry column here

    select top 1 * from (select top 2 * from tablename order by columnname desc) aliastablename order by aliastablename.columnname asc

    note - if you want to find out the nth then replace 2 by nth in subquery

  28. Nelson
    Posted 3/19/2008 at 4:23 am | Permalink

    query for second largest salary

    select min(sal) from employee where sal in(select distinct top 2 sal from employee order by sal desc)

  29. venu
    Posted 5/1/2008 at 4:03 pm | Permalink

    both primary and unique enforces uniqueness of a column on which they are defined but by default primary key creates a clustered index where as unique key creates a non clustered index and major diff is primary key does not allow any nulls where as unique allows one null only

  30. Mohd
    Posted 6/14/2008 at 3:02 am | Permalink

    can any body explain what is constraint?

  31. Sanjay Sinkar
    Posted 12/29/2008 at 8:06 am | Permalink

    /*—————————————
    Query that display second largest salary
    —————————————-*/
    SELECT MIN(Salary) AS Salary
    FROM Employee
    WHERE Salary IN ( SELECT TOP 2
    Salary
    FROM Employee
    ORDER BY Salary DESC )
    ORDER BY Salary DESC

  32. Sanjay Sinkar
    Posted 12/29/2008 at 9:49 am | Permalink

    /*———————————————
    77. How do you find the number of rows in a table?
    ———————————————*/

    SELECT COUNT(*)
    FROM

    OR
    /* This query will return data faster than previous*/
    SELECT rows
    FROM sysindexes WITH ( NOLOCK )
    WHERE id = OBJECT_ID()
    AND IndId < 2

  33. Sanjay Sinkar
    Posted 12/29/2008 at 9:57 am | Permalink

    Sorry, Table name missed in previous response no.234
    *———————————————
    77. How do you find the number of rows in a table?
    ———————————————*/

    SELECT COUNT(*)
    FROM TableName

    OR
    /* This query will return data faster than previous*/
    SELECT rows
    FROM sysindexes WITH ( NOLOCK )
    WHERE id = OBJECT_ID(’TableName’)
    AND IndId < 2

  34. Posted 1/28/2009 at 12:48 pm | Permalink

    Our MS Server 2000 changed date from Jan to Feb on the 19th Jan. For this one day, all date elements have changed from 1/19/2009 to 2/19/2009 as an example. I have found the tables that contain this data but I need the update command that will accomplish this. Problem is that some fields have the date and time combinded into one field. Example

    transDateTime
    02/19/2009 3:14:23 PM
    02/19/2009 9:10:54 PM
    02/19/2009 2:01:22 AM
    etc, etc

    What command can I issue against this table to replace the date with 01/19/2009 but still keep the times intact?

  35. Siva
    Posted 1/28/2009 at 11:01 pm | Permalink

    How to find top 2 salries of employees in each department ?

  36. Aman
    Posted 1/30/2009 at 3:01 am | Permalink

    Hi all,
    How to determine how many instances of SQL Server are installed on a computer?

  37. Aman
    Posted 1/30/2009 at 3:05 am | Permalink

    I created an object in one database,later i forgot the database name in which i created that object.There are so many databases in the serevr….is there any query to find out the database in which i created my object.

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  1. [...] Source: MS SQL Server interview questions Click for more. Lucky for me I wasn’t asked such question. This one always gets asked. For a while the database interview questions were limited to Oracle and generic database design questions. This is a set of more than a hundred Microsoft SQL Server interview questions. Some questions are open-ended, and some do not have answers. [...]

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