[thelist] SQL: Negative Join?

Sean G. ethanol at mathlab.sunysb.edu
Sun Sep 28 20:49:18 CDT 2003


Howdy,

Joshua was spot on with his reply.  I just want to butt in with a quick remark
as to why your query was not the solution to your problem.

>
>SELECT k.columns
>FROM keepers k
>LEFT JOIN tossers t
>    ON k.client <> t.client;
>

There's nothing wrong with using an inequality, or any other criteria, in a
JOIN.  However, in this case let's say k.client contains:

Joe
Bob
Sue

and t.client contains:

Joe
Frank
Kelly
Bob

Bob is in both lists, but Bob <> Joe.  Also, Bob <> Frank and Bob <> Kelly.

So while you could ask, give me any and all clients from k where there exists a
client from t that is not equal, what you really want is, give me clients from
k where there does not exist a client from t that is equal.


HTH,


Sean G.



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