Question

I have a query that looks like this:

use [dbName]

DECLARE @profile_id int
SET @profile_id = 18
DECLARE @test int

SET @test = (SELECT user_profile_id FROM tbl_profiles WHERE id = @profile_id)

SELECT @test as test

if @test = NULL
    SELECT 1

else 
    SELECT 2

I know that the value in the table is null, and I can see that @test is correctly being set to that value because the first SELECT shows:

 |test
1|NULL

However, in the IF condition the variable is not being treated as NULL because only the third SELECT is returned, showing:

 |(no column name)
1| 2

Why is that?

Answer 1

You need to use IS NULL (not = NULL)

if @test IS NULL
    SELECT 1

else 
    SELECT 2

You can never compare NULL with the “regular” comparison operators – you always have to use IS NULL or IS NOT NULL only.

And NULL really isn’t a value per se – it’s the absence of a value…