This provides a SQL Server FAQS-9 which are of "Difference between" kind

1. 1.Difference between VARCHAR and NVARCHAR in SQL Server
S.No Varchar[(n)] NVarchar[(n)]
1 Basic Definition: Basic Definition:
Non-Unicode Variable Length UNicode Variable Length character
character data type. data type. It can store both non-
Unicode and Unicode (i.e. Japanese,
Example: Korean etc) characters.
DECLARE @FirstName AS
VARCHAR(50) = ‘UMAR’ Example:
SELECT @FirstName DECLARE @FirstName AS
NVARCHAR(50)= ‘UMAR’
SELECT @FirstName
2 No. of Bytes required for each No. of Bytes required for each
character: character:
It takes 1 byte per character It takes 2 bytes per Unicode/Non-
Unicode character.
Example:
DECLARE @FirstName AS Example:
VARCHAR(50) = ‘UMAR’ DECLARE @FirstName AS
SELECT @FirstName AS NVARCHAR(50)= ‘UMAR’
FirstName,DATALENGTH(@Firs SELECT @FirstName AS
tName) AS Length FirstName,DATALENGTH(@FirstNa
me) AS Length
Result:
FirstName Length Result:
UMAR 4 FirstName Length
UMAR 8
3 Optional Parameter n range: Optional Parameter n range:
Optional Parameter n value can be Optional Parameter n value can be
from 1 to 8000.Can store from 1 to 4000.Can store maximum
maximum 8000 Non-Unicode 4000 Unicode/Non-Unicode characters
characters.
4 If Optional Parameter n is not If Optional Parameter n is not
specified in the variable specified in the variable declaration
declaration or column or column definition:
definition:
If Optional parameter value n is not
If Optional parameter value is not specified in the variable declaration or
specified in the variable column definition then it is considered
declaration or column definition as 2
then it is considered as 1.
Example:
Example: DECLARE @firstName NVARCHAR
DECLARE @firstName =‘UMAR’
VARCHAR =‘UMAR’ SELECT @firstName

2. SELECT @firstName FirstName,DATALENGTH(@firstNa
FirstName,DATALENGTH(@firs me) Length
tName) Length
Result:
Result: FirstName Length
FirstName Length U2
U1
5 If Optional Parameter n is not If Optional Parameter n is not
specified in while using specified in while using
CAST/CONVERT functions: CAST/CONVERT functions:
When this optional parameter n is When this optional parameter n is not
not specified while using the specified while using the CAST
CAST/CONVERT functions, then CONVERT functions, then it is
it is considered as 30. considered as 30.
Example: Example:
DECLARE @firstName DECLARE @firstName
VARCHAR(35) =‘UMAR ASIA NVARCHAR(35) =‘UMAR ASIA
INDIA TAMIL NADU INDIA TAMIL NADU
CUDDALORE’ CUDDALORE’
SELECT CAST(@firstName AS SELECT CAST(@firstName AS
VARCHAR) NVARCHAR)
FirstName,DATALENGTH(CAS FirstName,DATALENGTH(CAST(@f
T(@firstName AS VARCHAR)) irstName AS NVARCHAR)) Length
Length
Result:
Result: FirstName Length
FirstName Length UMAR ASIA INDIA TAMIL NADU
UMAR ASIA INDIA TAMIL CUD 60
NADU CUD 30
7 Which one to use? Which one to use?
If we know that data to be stored If we know that data to be stored in the
in the column or variable doesn’t column or variable can have Unicode
have any Unicode characters. characters.
8 Storage Size: Storage Size:
Takes no. of bytes equal to the no. Takes no. of bytes equal to twice the
of Characters entered plus two no. of Characters entered plus two
bytes extra for defining offset. bytes extra for defining offset.

3. 2.Difference between SQL Server and MySQL
S.No SQL Server MySQL
1 Current Date and Time: Current Date and Time:
SELECT GETDATE() SELECT NOW()
Optionally: Use CURDATE() for the
date only.
2 Limiting Results: Limiting Results:
SELECT TOP 10 * FROM table SELECT * FROM table WHERE id =
WHERE id = 1 1 LIMIT 10
3 Date Field Default Value: Date Field Default Value:
DATETIME DEFAULT DATETIME fields cannot have a
GETDATE() default value, i.e. "GETDATE()"
We must use your INSERT statement
to specify CURDATE() for the field.
Optionally: Use datatype
TIMESTAMP DEFAULT
CURRENT_TIMESTAMP
4 Character Length: Character Length:
LEN() CHARACTER_LENGTH()
Aliases: CHAR_LENGTH(),
LENGTH()
5 Character Replace: Character Replace:
REPLACE() works case REPLACE() works case sensitively
insensitively
6 Trim Functions: Trim Functions:
LTRIM() and RTRIM() TRIM()
7 String Concatenation: String Concatenation:
CONCATENATION USING + CONCAT(string, string), which
(Does not automatically cast accepts two or more arguments.
operands to compatible types) (Automatically casts values into types
which can be concatenated)
8 Auto Increment Field Auto Increment Field Definition:
Definition:

4. tablename_id INTEGER
tablename_id INT IDENTITY AUTO_INCREMENT PRIMARY
PRIMARY KEY KEY
9 Get a List of Tables: Get a List of Tables:
SP_TABLES SHOW TABLES
10 Get Table Properties: Get Table Properties:
HELP tablename DESCRIBE tablename
11 Get Database Version: Get Database Version:
SELECT @@VERSION SELECT VERSION()
12 Recordset Paging: Recordset Paging:
Recordset paging done by client Add to end of SQL: "LIMIT " &
side-ADO (very involved) ((intCurrentPage-1)*intRecsPerPage)
& ", " & intRecsPerPage
LIMIT: The first argument specifies
the offset of the first row to return, and
the second specifies the maximum
number of rows to return. The offset of
the initial row is 0 (not 1).
13 Get ID of Newest Inserted Get ID of Newest Inserted Record:
Record:
Two step process:
SET NOCOUNT ON; INSERT 1. Execute your statement:
INTO...; SELECT objConn.Execute("INSERT INTO...")
id=@@IDENTITY; SET 2. Set objRS =
NOCOUNT OFF; objConn.Execute("SELECT
LAST_INSERT_ID() AS ID")
14 Get a Random Record: Get a Random Record:
SELECT TOP 1 * FROM Users SELECT * FROM Users ORDER BY
ORDER BY NEWID() RAND() LIMIT 1
15 Generate a Unique GUID: Generate a Unique GUID:
SELECT NEWID() SELECT UUID()

5. 3.Difference between SET QUOTED_IDENTIFIER ON and SET QUOTED_IDENTIFIER
OFF in SQL Server
S.No SET QUOTED_IDENTIFIER SET QUOTED_IDENTIFIER OFF
ON
1 Characters Enclosed within Characters Enclosed within double
double quotes: quotes:
is treated as Identifier is treated as Literal
2 Try using Characters Enclosed Try using Characters Enclosed
within double quotes as within double quotes as identifier:
identifier:
Fails
Works Example: Below statement to create a
Example: Below statement to table with table name “Table” Fails.
create a table with table name SET QUOTED_IDENTIFIER OFF
“Table” succeeds. GO
SET QUOTED_IDENTIFIER ON CREATE TABLE dbo.”Table”
GO (id int,”Function” VARCHAR(20))
CREATE TABLE dbo.”Table” GO
(id int,”Function” Error Message:
VARCHAR(20)) GO Msg 102, Level 15, State 1,
Line 1 Incorrect syntax near ‘Table’.
3 Try using Characters Enclosed Try using Characters Enclosed
within double quotes as Literal: within double quotes as Literal:
Fails Works
Example: Below statement fails. Example: Below Statement Works.
SET QUOTED_IDENTIFIER ON SET QUOTED_IDENTIFIER OFF
GO GO
SELECT “BIRADAR” SELECT “UMAR”
Error Message:
Msg 207, Level 16, State 1,
Line 1 Invalid column name
‘UMAR’.
4 Characters Enclosed within Characters Enclosed within single
single quotes: quotes:
is treated as Literal is treated as Literal
Example: Example:
SET QUOTED_IDENTIFIER ON SET QUOTED_IDENTIFIER ON
GO GO
SELECT ‘UMAR’ SELECT ‘UMAR’
5 How to find all the objects How to find all the objects which are
which are created with SET created with SET

6. QUTOED_IDENTIFIER QUTOED_IDENTIFIER ON/OFF:
ON/OFF:
Below Statement can be used to find
Below Statement can be used to all the objects created with SET
find all the objects created with QUTOED_IDENTIFIER setting as
SET QUTOED_IDENTIFIER OFF:
setting as ON:
SELECT OBJECT_NAME (object_id)
SELECT OBJECT_NAME FROM sys.sql_modules WHERE
(object_id) FROM uses_quoted_identifier = 0
sys.sql_modules WHERE
uses_quoted_identifier = 1
4.Difference between DateTime and DateTime2 DataType
S.No DateTime DateTime2[(n)]
1 Min Value: 1753-01-01 00:00:00 Min Value: 0001-01-01 00:00:00
2 Max Value: Max Value:
9999-12-31 23:59:59.997 9999-12-31 23:59:59.9999999
3 Storage Size: Storage Size:
8 Bytes 6 to 8 bytes
Note: Parameter n is optional and if it
is not specified then fractional seconds
precision is 7 digit and it can be from 0
to 7 digit.
For fractional seconds precision <3,
takes 6 bytes
For fractional seconds precision 3 or 4
it will take 7 bytes
For fractional seconds precision >4 it
will take 8 bytes
4 Usage: Usage:
Declare @now datetime Declare @now datetime2(7)
5 Current Date and Time Current Date and Time function:
function:
SYSDATETIME()- It returns DB
GetDate() – It returns DB Current Current Date and Time of DateTime2
Date and Time of DateTime Data Data Type
Type
Example: SELECT SYSDATETIME()
Example: SELECT GETDATE() Result: 2011-09-16 13:23:18.7676720

7. Result: 2011-09-16 13:23:18.767
6 +/- days: +/- days:
WORKS FAILS – Need to use only DateAdd
Example: DECLARE function
@nowDateTime DATETIME = Example: DECLARE
GETDATE() @nowDateTime2 DATETIME2=
SELECT @nowDateTime + 1 SYSDATETIME()
Result: 2011-09-17 13:44:31.247 SELECT @nowDateTime2+1
Result: Msg 206, Level 16, State 2,
Line 2
Operand type clash: datetime2 is
incompatible with int
7 Compliance: Compliance:
Is not an ANSI/ISO compliant Is an ANSI/ISO compliant
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