How to use NULL or empty string in SQL

In sproc, you can use the following condition:

DECLARE @USER_ID VARCAHR(15)=NULL --THIS VALUE IS NULL OR EMPTY DON'T MATTER
IF(COALESCE(@USER_ID,'')='')
PRINT 'HUSSAM'

by this function:

ALTER FUNCTION [dbo].[isnull](@input nvarchar(50),@ret int = 0)
RETURNS int
AS
BEGIN

return (case when @input='' then @ret when @input is null then @ret else @input end)

END

and use this:

dbo.isnull(value,0)

<!-- language: sql-->

SELECT * FROM DBO.AGENDA
WHERE
--IF @DT_START IS NULL OR EMPTY
( ISNULL( @DT_START,'' ) = '' AND DT_START IS NOT NULL ) -- GET ALL DATE
OR --ELSE
( DT_START >= @DT_START ) --FILTER

-- MORE FILTER

SELECT * FROM DBO.AGENDA
WHERE
( ( ISNULL( @DT_START,'' ) = '' AND DT_START IS NOT NULL ) OR ( DT_START >= @DT_START ) )
AND
DT_END < GETDATE()

youe check null With IS NULL and string Empty With LEN(RTRIM(LTRIM(Column))) = 0
in

SELECT *
FROM AppInfra.Person
WHERE LEN(RTRIM(LTRIM(NationalCode))) = 0 OR NationalCode IS NULL

my best solution :

WHERE
COALESCE(char_length(fieldValue), 0) = 0

COALESCE returns the first non-null expr in the expression list().

if the fieldValue is null or empty string then: we will return the second element then 0.

so 0 is equal to 0 then this fieldValue is a null or empty string.

in python for exemple:

def coalesce(fieldValue):
if fieldValue in (null,''):
return 0

good luck

select
isnull(column,'') column, *
from Table
Where column = ''

If you need it in **SELECT** section can use like this.

SELECT ct.ID,
ISNULL(NULLIF(ct.LaunchDate, ''), null) [LaunchDate]
FROM [dbo].[CustomerTable] ct

You can replace the `null` with your substitution value.

You can use ***in*** as another method

Select *
From Table
Where column in(null, '')