Comparing Column Values in T-SQL

Okay… so here's the scenario. I have two different tables in a SQL Database, where I need to compare both tables, and find all values in Table B that do not exist in Table A. There are two ways to do this. One with a JOIN, and one with a "NOT EXISTS" Clause:

 

Method 1:

 

SELECT b.[ColumnName]

    FROM DBName.dbo.tblB b

    LEFT OUTER JOIN DBName.dbo.tblA a

    ON b.[ColumnName] = a.[ColumnName]

    WHERE a.[ColumnName] IS NULL

    GROUP BY b.[ColumnName];

Method 2:

 

SELECT b.[ColumnName]

    FROM DBName.dbo.tblB b

    WHERE NOT EXISTS

    (

        SELECT *

            FROM DBName.dbo.tblA

            WHERE a.[ColumnName] = b.[ColumnName]

    )

    GROUP BY b.[ColumnName];

 

I hope this helps someone! My malformed queries have been driving me nuts all week…

Comments

• Anonymous
  January 01, 2003
  Excellent !! I've been wracking my brains for ages trying to figure out how to do this (new to SQL). I actually have to work out what does not exist in one table when compared to 2 others, but taking the above and allowing for the extra table has solved my problem. I had played around with LEFT OUTER JOIN, but did not consider the comparison with NULL !! Many thanks.

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