Re: EXISTS vs IN vs OUTER JOINS - Mailing list pgsql-performance

On Thu, 19 Dec 2002 15:19:21 -0800, "Josh Berkus" <josh@agliodbs.com>
wrote:
>SELECT t1.*
>FROM table1 t1
>  LEFT JOIN table2 t2 ON t1.xid = t2.xid
>WHERE t2.label IS NULL

Josh, also note that Tomasz did something like

SELECT t1.*
FROM table1 t1
  LEFT JOIN table2 t2 ON t1.xid = t2.xid
WHERE t2.xid IS NULL
         ^^^
This special trick guarantees that you get exactly the rows from t1
not having a matching row in t2, because a NULL xid in t2 would not
satisfy the condition t1.xid = t2.xid.

Servus
 Manfred