This is really simple, but simple is what I am all about. When using SELECT DISTINCT from huge tables with many joins, it forces a full table scan and can slow down a query.
SELECT DISTINCT blah blah blah blah blah blah blah
FROM A,B,C
WHERE A.CUST_ID = B.CUST_ID
AND blah blah blah blah blah
AND blah
Would be inefficient
To get around this put the distinct on the outside of a subquery:
Select Distinct blah, blah, blah, blah
FROM
(SELECT blah, blah, blah, blah, blah, blah, blah,
FROM A,B,C
WHERE A.CUST_ID = B.CUST_ID
AND blah AND blah AND blah
AND blah )
4:05:18 PM
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