[wp-trac] [WordPress Trac] #17582: Problems with duplicated users

[WordPress Trac]

#17582: Problems with duplicated users
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 Reporter:  scribu        |       Owner:  ryan
     Type:  defect (bug)  |      Status:  closed
 Priority:  normal        |   Milestone:  3.2
Component:  Query         |     Version:
 Severity:  normal        |  Resolution:  fixed
 Keywords:  has-patch     |
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Comment (by Denis-de-Bernardy):

 Replying to [comment:29 scribu]:
 > greuben's test suggested that DISTINCT is faster.

 That was because he was grouping by id. In other words it's ordered twice.

 If you order by display_name, the group by/order by should be:

 {{{
 GROUP BY display_name, ID
 ORDER BY display_name, ID
 }}}

 That way they'll only need to be ordered once, and the extra ID sub-
 ordering will strip out the dups. Best I'm aware MySQL won't do this
 automatically when using distinct, though I may be wrong (in which case it
 would certainly explain why it was faster to use distinct).

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Ticket URL: <http://core.trac.wordpress.org/ticket/17582#comment:30>
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