Question

First a quick explanation: I am actually dealing with four tables and mining data from different places but my problem comes down to this seemingly simple concept and yes I am very new to this…

I have two tables (one and two) that both have ID columns in them. I want to query only the ID columns that are in table two only, not in both. As in..

Select ID
From dbo.one, dbo.two
Where dbo.two != dbo.one

I actually thought this would work but I’m getting odd results. Can anyone help?

Answer 1

SELECT t2.ID
    FROM dbo.two t2
    WHERE NOT EXISTS(SELECT NULL
                         FROM dbo.one t1
                         WHERE t2.ID = t1.ID)

This could also be done with a LEFT JOIN:

SELECT t2.ID
    FROM dbo.two t2
        LEFT JOIN dbo.one t1
            ON t2.ID = t1.ID
    WHERE t1.ID IS NULL