SQL HELP - Conditional where clause based on a BIT variable - SQL Server

Question

I need help writing a conditional where clause. here is my situation:

I have a bit value that determines what rows to return in a select statement. If the value is true, I need to return rows where the import_id column is not null, if false, then I want the rows where the import_id column is null.

My attempt at such a query (below) does not seem to work, what is the best way to accomplish this?

DECLARE @imported BIT

SELECT id, import_id, name FROM Foo WHERE
    (@imported = 1 AND import_id IS NOT NULL)
    AND (@imported = 0 AND import_is IS NULL)

Thanks.

Answer 1

Change the AND to OR

DECLARE @imported BIT

SELECT id, import_id, name FROM Foo WHERE
    (@imported = 1 AND import_id IS NOT NULL)
    OR (@imported = 0 AND import_is IS NULL)

Decomposing your original statement

you have essentially written

    @imported = 1 
    AND import_id IS NOT NULL
    AND @imported = 0 
    AND import_is IS NULL

wich is equivalent to

    @imported = 1 AND @imported = 0 
    AND import_id IS NOT NULL AND import_is IS NULL

what results in two pair of clauses that completely negate each other

Answer 2

I think you meant

SELECT id, import_id, name FROM Foo WHERE
    (@imported = 1 AND import_id IS NOT NULL)
    OR (@imported = 0 AND import_is IS NULL)
    ^^^