1. What are the two authentication modes in SQL Server?
There are two authentication modes –
·
Windows Mode
·
Mixed Mode
Modes can
be changed by selecting the tools menu of SQL Server configuration properties
and choose security page.
2. What Is SQL Profiler?
SQL Profiler is a tool which allows
system administrator to monitor events in the SQL server. This is mainly
used to capture and save data about each event of a file or a table for
analysis.
3. What is recursive stored procedure?
SQL Server supports recursive stored
procedure which calls by itself. Recursive stored procedure can be defined as a
method of problem solving wherein the solution is arrived repetitively. It can
nest up to 32 levels.
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CREATE PROCEDURE [dbo].[Fact]
(
@Number Integer,
@RetVal Integer OUTPUT
)
AS
DECLARE @In Integer
DECLARE @Out Integer
IF @Number != 1
BEGIN
SELECT @In = @Number – 1
EXEC Fact @In, @Out OUTPUT - Same stored procedure has been called again(Recursively)
SELECT @RetVal = @Number
* @Out
END
ELSE
BEGIN
SELECT @RetVal = 1
END
RETURN
GO
|
4. What are the differences between local and global
temporary tables?
·
Local temporary tables are
visible when there is a connection, and are deleted when the connection is
closed.
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CREATE TABLE #<tablename>
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·
Global temporary tables are
visible to all users, and are deleted when the connection that created it is
closed.
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CREATE TABLE ##<tablename>
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5. What is CHECK constraint?
A CHECK constraint can be applied to a
column in a table to limit the values that can be placed in a column. Check
constraint is to enforce integrity.
6. Can SQL servers linked to other servers?
SQL
server can be connected to any database which has OLE-DB provider to give a link. Example: Oracle has
OLE-DB provider which has link to connect with the SQL server group.
7. What is sub query and its properties?
A sub-query is a query which can be
nested inside a main query like Select, Update, Insert or Delete statements.
This can be used when expression is allowed. Properties of sub query can be
defined as
·
A sub query should not have order by
clause
·
A sub query should be placed in the
right hand side of the comparison operator of the main query
·
A sub query should be enclosed in
parenthesis because it needs to be executed first before the main query
·
More than one sub query can be included
8. What are the types of sub query?
There are three types of sub query –
·
Single row sub query which returns only
one row
·
Multiple row sub query which returns
multiple rows
·
Multiple column sub query which returns
multiple columns to the main query. With that sub query result, Main query will
be executed.
9. What is SQL server agent?
The SQL Server agent plays a vital
role in day to day tasks of SQL server administrator(DBA). Server agent’s
purpose is to implement the tasks easily with the scheduler engine which allows
our jobs to run at scheduled date and time.
10. What are scheduled tasks in SQL Server?
Scheduled tasks or jobs are used to
automate processes that can be run on a scheduled time at a regular interval.
This scheduling of tasks helps to reduce human intervention during night time
and feed can be done at a particular time. User can also order the tasks in
which it has to be generated.
11. What is COALESCE in SQL Server?
COALESCE is used to return first
non-null expression within the arguments. This function is used to return a
non-null from more than one column in the arguments.
Example –
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Select COALESCE(empno, empname, salary) from employee;
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12. How exceptions can be handled in SQL
Server Programming?
Exceptions are handled using TRY—-CATCH
constructs and it is handles by writing scripts inside the TRY block and error
handling in the CATCH block.
13. What is the purpose of FLOOR function?
FLOOR function is used to round up a
non-integer value to the previous least integer. Example is given
Returns 6.
14. Can we check locks in database? If so, how
can we do this lock check?
Yes, we can check locks in the database.
It can be achieved by using in-built stored procedure called sp_lock.
15. What is the use of SIGN function?
SIGN function is used to determine
whether the number specified is Positive, Negative and Zero. This will return
+1,-1 or 0.
Example –
16. What is a Trigger?
Triggers are used to execute a batch of
SQL code when insert or update or delete commands are executed against a table.
Triggers are automatically triggered or executed when the data is modified. It
can be executed automatically on insert, delete and update operations.
17. What are the types of Triggers?
There are four types of triggers and
they are:
·
Insert
·
Delete
·
Update
·
Instead of
18. What is an IDENTITY column in insert
statements?
IDENTITY column is used in table columns
to make that column as Auto incremental number or a surrogate key.
19. What is Bulkcopy in SQL?
Bulkcopy is a tool used to copy large
amount of data from Tables. This tool is used to load large amount of data in SQL
Server.
20. What will be query used to get the list of
triggers in a database?
Query to get the list of triggers in
database-
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Select * from sys.objects where type=’tr’
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21. What is the difference between UNION and
UNION ALL?
UNION statement is mainly used to
combine the tables including the duplicate rows and UNION ALL combine but does
not look for duplicate rows. With this, UNION ALL will be very faster than
UNION statements.
22. How Global temporary tables are represented
and its scope?
Global temporary tables are represented
with ## before the table name. Scope will be the outside the session whereas
local temporary tables are inside the session. Session ID can be found using
@@SPID.
23. What are the differences between Stored
Procedure and the dynamic SQL?
Stored Procedure is a set of statements
which is stored in a compiled form. Dynamic SQL is a set of statements that
dynamically constructed at runtime and it will not be stored in a Database and
it simply execute during run time.
24. What is Collation?
Collation is defined to specify the sort
order in a table. There are three types of sort order –
1.
Case sensitive
2.
Case Insensitive
3.
Binary
25. How can we get count of the number of records
in a table?
Following are the queries can be used to
get the count of records in a table –
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Select * from <tablename> Select
count(*) from <tablename> Select rows from sysindexes whereid=OBJECT_ID(tablename) and indid<2
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26. What is the command used to get the version of SQL
Server?
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Select SERVERPROPERTY(‘productversion’)
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is used to get the version of SQL
Server.
27. What is UPDATE_STATISTICS command?
UPDATE_STATISTICS command is used to
update the indexes on the tables when there is a large amount of deletions or
modifications or bulk copy occurred in indexes.
28. What is the use of SET NOCOUNT ON/OFF
statement?
By default, NOCOUNT is set to OFF and it
returns number of records got affected whenever the command is getting
executed. If the user doesn’t want to display the number of records affected,
it can be explicitly set to ON- (SET NOCOUNT ON).
29. Which SQL server table is used to hold the
stored procedure scripts?
Sys.SQL_Modules is a SQL Server table
used to store the script of stored procedure. Name of the stored procedure is
saved in the table called Sys.Procedure.
30. What are Magic Tables in SQL Server?
Insert and Delete tables are created
when the trigger is fired for any DML command. Those tables are called Magic
Tables in SQL Server. These magic tables are used inside the triggers for data
transaction.
31. What is the difference between SUBSTR and
INSTR in the SQL Server?
The SUBSTR function is used to return
specific portion of string in a given string. But, INSTR function gives
character position in a given specified string.
Gives result as Smi
Gives 3
as result as I appears in 3rd position of the string
32. What is the use of =,==,=== operators?
= is used to assign one value or
variable to another variable. == is used for comparing two strings or numbers.
=== is used to compare only string with the string and number with numbers.
33. What is ISNULL() operator?
ISNULL function is used to check whether
value given is NULL or not NULL in sql server. This function also provides to
replace a value with the NULL.
34. What is the use of FOR Clause?
FOR clause is mainly used for XML and
browser options. This clause is mainly used to display the query results in XML
format or in browser.
35. What will be the maximum number of index per
table?
100 Index can be used as maximum number
per table. 1 Clustered Index and 999 Non-clustered indexes per table can be
used in SQL Server.
36. What is the difference between COMMIT and
ROLLBACK?
Every statement between BEGIN and COMMIT
becomes persistent to database when the COMMIT is executed. Every statement
between BEGIN and ROOLBACK are reverted to the state when the ROLLBACK was
executed.
37. What is the difference between varchar and
nvarchar types?
Varchar and nvarchar are same but the
only difference is that nvarhcar can be used to store Unicode characters for
multiple languages and it also takes more space when compared with varchar.
38. What is the use of @@SPID?
A @@SPID returns the session ID of the current
user process.
39. What is the command used to Recompile the
stored procedure at run time?
Stored Procedure can be executed with
the help of keyword called RECOMPILE.
Example
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Exe <SPName> WITH RECOMPILE
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Or we can include WITHRECOMPILE in the
stored procedure itself.
40. How to delete duplicate rows in SQL Server?
Duplicate rows can be deleted using CTE
and ROW NUMER feature of SQL Server.
41. Where are SQL Server user names and passwords
stored in SQL Server?
User Names and Passwords are stored in
sys.server_principals and sys.sql_logins. But passwords are not stored in
normal text.
42. What is the difference between GETDATE and
SYSDATETIME?
Both are same but GETDATE can give time
till milliseconds and SYSDATETIME can give precision till nanoseconds. SYSDATE
TIME is more accurate than GETDATE.
43. How data can be copied from one table to
another table?
INSERT INTO SELECT
This command is used to insert data into
a table which is already created.
SELECT INTO
This command is used to create a new
table and its structure and data can be copied from existing table.
44. What is TABLESAMPLE?
TABLESAMPLE is used to extract sample of
rows randomly that are all necessary for the application. The sample rows taken
are based on the percentage of rows.
45. Which command is used for user defined error
messages?
RAISEERROR is the command used to
generate and initiates error processing for a given session. Those user defined
messages are stored in sys.messages table.
46. What do mean by XML Datatype?
XML data type is used to store XML
documents in the SQL Server database. Columns and variables are created and
store XML instances in the database.
47. What is CDC?
CDC is abbreviated as Change Data
Capture which is used to capture the data that has been changed recently. This
feature is present in SQL Server 2008.
48. What is SQL injection?
SQL injection is an attack by malicious
users in which malicious code can be inserted into strings that can be passed
to an instance of SQL server for parsing and execution. All statements have to
checked for vulnerabilities as it executes all syntactically valid queries that
it receives.
Even parameters can be manipulated by
the skilled and experienced attackers.
49. What are the methods used to protect against
SQL injection attack?
Following are the methods used to
protect against SQL injection attack:
·
Use Parameters for Stored Procedures
·
Filtering input parameters
·
Use Parameter collection with Dynamic
SQL
·
In like clause, user escape characters
50. What is Filtered
Index?
Filtered Index is used to filter some
portion of rows in a table to improve query performance, index maintenance and
reduces index storage costs. When the index is created with WHERE clause, then
it is called Filtered Index
Difference between stored procedure and function
1) Procedure can return zero or n values whereas function can return one value which is mandatory.
2) Procedures can have input, output parameters for it whereas functions can have only input parameters.
3) Procedure allows select as well as DML statement in it whereas function allows only select statement in it.
4) Functions can be called from procedure whereas procedures cannot be called from function.
5) Exception can be handled by try-catch block in a procedure whereas try-catch block cannot be used in a function.
6) We can go for transaction management in procedure whereas we can't go in function.
7) Procedures cannot be utilized in a select statement whereas function can be embedded in a select statement.
Index types in SQL Server
Clustered Index
Only 1 allowed per table physically rearranges the data in the table to confirm to the index constraints for use on columns that are frequently searched for ranges of data for use on columns with low selectivity.
Non-Clustered Index
Up to 249 allowed per table creates a separate list of key values with pointers to the location of the data in the data pages For use on columns that are searched for single values
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.
What are differences between function and stored procedure?
Ans:
1) Function returns only one value but procedure returns one or more than one value.
2) Function can be utilized in select statements but that is not possible in procedure.
3) Procedure can have an input and output parameters but function has only input parameters only.
4) Exceptions can be handled by try catch block in procedures but that is not possible in function.
What is the difference between primary key and unique key with not null?
Ans: There is no difference between primary key and unique key with not null.
Write a sample query for self join?
Ans: Select e1.ename, e2.empid from emp e1, emp e2 where e1.empid=e2.mgrid;
Can we change the index of primary key on table?
Ans: No
How to change the name of the table or stored procedure in sql?
Ans: sp_rename oldtablename newtablename
For changing the column name
Sp_rename ‘tablename.[Oldcolumnname]’,’newcolumnname’,’Column’
Ex:sp_rename ‘tblemp.first’,’namechange’,’Column’
How to find out which index is defined on table?
Ans: sp_helpindex tablename
Can you write the program to find the length of string without using library function?
Ans: for (int i=0; str[i]!=”\n”; i++)
{
Count++;
}
What is the difference between scope_identity() and current_identity()?
Ans: Scope_identity and current _identity both are similar and it will return the last identity value generated in the table.
Scope_Identity will return the identity value in table that is currently in scope
What are difference between truncate and delete?
Ans: 1) Delete keep the lock over each row where Truncate keeps the lock on table not on all the row.
2) Counter of the Identity column is reset in Truncate where it is not reset in Delete.
3) Trigger is not fired in Truncate where as trigger is fired in Delete.
4) In TRUNCATE we cannot rollback.
5) In DELETE we can rollback
