As in, if the first part of the query (before the EXCEPT clause), without the DISTINCT, yielded
yahoo.com yahoo.com
would the query reduce that to a single yahoo.com regardless of whether it showed up in the EXCEPT clause?
-tfo
-- Thomas F. O'Connell Co-Founder, Information Architect Sitening, LLC http://www.sitening.com/ 110 30th Avenue North, Suite 6 Nashville, TN 37203-6320 615-260-0005
On Dec 2, 2004, at 10:26 AM, Tom Lane wrote:
=?iso-8859-15?Q?Pierre-Fr=E9d=E9ric_Caillaud?= <[EMAIL PROTECTED]> writes:I may be mistaken, but you may be doing the same thing twice : you're basically writing :
SELECT DISTINCT X WHERE Y EXCEPT SELECT DISTINCT X WHERE NOT Y Is this not a way to get an empty result set ?
No, because some X values may appear in rows where Y, and also in rows where NOT Y.
The DISTINCTs are wastes of time, though, because EXCEPT implies elimination of duplicates.
regards, tom lane
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