On Thu, 2008-02-21 at 23:34 +0000, David Lee wrote: > I ran EXPLAIN and it showed that the path did not use the index, so I ran:
Your expectation that this would use an index is unfortunately not correct. We need to check visibility on the table rows to do the query. We choose to do this by doing a sort and then a unique operation. That's the most efficient plan when there are potentially many unique values. In the case you mention it would be faster for us to skip through the index retrieving at most one row from each value in the index. We don't currently do that, but we could. However that plan would be restricted only to queries of the form SELECT DISTINCT column-list-of-index FROM table; so its probably not going to be optimised anytime soon. -- Simon Riggs 2ndQuadrant http://www.2ndQuadrant.com ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
