how to handle null value or empty string in Stored Procedure parameter in where condition

SELECT FName, LName
FROM tblAccounts
WHERE
  fname like (case when @fname = '' then fname else @fname end) and
  lname like (case when @lname = '' then lname else @lname end)

LIKE this above example i solved my Problem


thanks to all............

That logical condition is never going to work: WHERE operates on the row data, and you are purely asking to to decide based on parameter data which will not change from row to row - so it will either return all rows or no rows - it cannot filter the row data at all.

Probably, you want to use the parameters to compare against row data - but without knowing more about your system it's not possible to be more exact.
However, I would move the IS NULL outside my SELECT anyway:

DECLARE @P VARCHAR(10)
SET @P = ISNULL(@mParameter, 'M')

SELECT * FROM MyTable WHERE @P ='M'

But what you probably want to do is more along the lines of:

DECLARE @P VARCHAR(10)
SET @P = ISNULL(@mParameter, 'M')

SELECT * FROM MyTable WHERE Model=@P

You have not used the Columns in the where conditions inside the query.

WHERE (@mParameter = 'M' OR @mParameter IS NULL)
AND (@tParameter = 'T' OR @tParameter IS NULL)
AND (@gParameter = 123 OR @gParameter IS NULL)
AND (@nParameter = 'N' OR @nParameter IS NULL)

Here it should be Columns, not parameters.

WHERE (Column1 = 'M' OR Column1 IS NULL)
AND (Column2  = 'T' OR Column2  IS NULL)
AND (Column3  = 123 OR Column3  IS NULL)
AND (Column4  = 'N' OR Column4  IS NULL)