-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Simon Gray wrote: | John Fawcett wrote: |> Simon |> |> I doubt that splitting the queries will change whether an index is used. |> The potential index on mailbox_idnr is not a good one when there are |> many rows corresponding to mailbox_idnr. |> |> Did you try to explain the separated queries? The behaviour should be |> the same as in the combined select. |> |> John | John, | | It doesn't actually use the mailbox_idnr key (at least not in my | environment) it is using the mailbox_status instead. I think the problem | relies within mysql rather than dbmail here, mysql will internally use | its temptable algorithm on unions like this. | | http://bugs.mysql.com/bug.php?id=29244 | | You are correct, the behaviour is the same on each individual query | except the union result part. | Simon also, if you try an explain of the query on a mailbox with few messages, mysql will use the index on mailbox_idnr because (presumably) that is a better policy than range scan on mailbox_status if there are few matching index rows. John -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4-svn0 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org
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