what is the diffrence between Null and IsNull?

Hi,

Null means that the empty of value and isnull is used to check the value is null or not and isnull is using with where clause

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= NULL is always unknown (this is piece of 3 state logic), but WHERE clause treats it as false and drops from the result set. So for NULL you should use IS NULL

Reasons are described here: http://stackoverflow.com/questions/1843451/why-does-null-null-evaluate-to-false-in-sql-server

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Null is value whose presence is being check with Is Null

Declare @input varchar(10) = NULL

Select

		Case When @input IS NULL Then 'Null Present' Else 'Not Null'

		End As Result

Result
Null Present

Also there is a function call ISNULL which checks if NULL is present or not and if so replaces the NULL value with the default value being supplied

Declare @input varchar(10) = NULL

Select	ISNULL(@input,'Default value') As Result

Result
Defalt value

Best Regards,
Niladri Biswas

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NULL

NULL is supposed to be undefined, meaning you don't know what it could be. "" on the other hand is actually defining it is as
something; a blank value.

ISNULL
If your database is initializing the fields as "", then = NULL is the right way. If you use the keyword NULL, then ISNULL will correctly test for it.

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Hi,

Null means assign Null values .ISNull means check null or not


Regards

sriram

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Hi,

NULL means Empty or blank value.

ISNULL is a built-in function used to assign some values for NULL

For Example

select ISNULL(NULL,100)

Replace NULL into 100

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