Question

I’m working on a bigger problem, but have narrowed it down to this, in order to make this question easier to ask.

The following query:

Select * from User where Country = Country 

Will only return the rows where Country is not null. I would expect if Column1 is null it would return it because NULL = NULL.

Any input on why this is not working as I expect?

EDIT:

I am trying to do this:

Select * from User where Country = coalesce(@Country, Country)

If my variable @Country is null, I want it to pull everything.

Answer 1

SQL uses three valued logic (true, false, unknown) and comparisons to NULL (except for testing with the IS [NOT] NULL operator) evaluate as unknown not true as long as the session option ANSI_NULLS is on.

For a row to be returned from your query the WHERE clause needs to evaluate to true.

Following your edit you can use

Select * 
from User 
where @Country is null or Country = @Country
option (recompile)

To return all rows when @country is null. Although probably better just to break these up into 2 cases to avoid the recompile penalty.

IF @Country is null
Select * 
from User 
ELSE
Select * 
from User 
Where Country = @Country