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1. 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.

2. 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.

3. 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 

4. 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.

5. 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 

6. What are different types of Collation Sensitivity?

Case sensitivity -  A and a, B and b, etc.
• Accent sensitivityKana 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. 

7. 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.

8. 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.

9. 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.

10. 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

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

Properties of Sub-Query
    
    • A sub-query must be enclosed in the parenthesis.
    • A sub-query must be put in the right hand of the comparison operator, and
    • A sub-query cannot contain an ORDER-BY clause.
    • 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
    

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.

17. 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.

18. 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: 

• TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.
• 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. 
• 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.
• 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.
• TRUNCATE cannot be rolled back.
• TRUNCATE is DDL Command.
• TRUNCATE Resets identity of the table

• DELETE: 

• DELETE removes rows one at a time and records an entry in the transaction log for each deleted row. 
• 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.
• DELETE Can be used with or without a WHERE clause 
• DELETE Activates Triggers.
• DELETE can be rolled back.
• DELETE is DML Command.
• 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. 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.

24. 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. 

25. 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.

26. 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.

27. 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.

28. 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.

29. 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.

30. 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.

31. 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.

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

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

33. 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.