On 01/31/2013 04:41 AM, Timour Katchaounov wrote: > Igor, > > Let me know if I can push the patch below. It fixes the bug > according to our last discussion. If the number of group_list > elements was known, I could add a test already in the beginning > of the function, however such a counter doesn't exist, and I > didn't want to complicate the code just for this special case. > That's why the test is done where it is now. > > Timour > > > ------------------------------------------------------------ > revno: 3622 > revision-id: [email protected] > parent: [email protected] > fixes bug(s): https://mariadb.atlassian.net/browse/MDEV-641 > committer: [email protected] > branch nick: 5.3-md641 > timestamp: Thu 2013-01-31 14:00:40 +0200 > message: > Analysis: > Range analysis discoveres that the query can be executed via loose > index scan for GROUP BY. > Later, GROUP BY analysis fails to confirm that the GROUP operation can > be computed via an > index because there is no logic to handle duplicate field references > in the GROUP clause. > As a result the optimizer the optimizer produces an inconsistent plan. > It constructs a > temporary table, but on the other hand the group fields are not set to > point there. > > Solution: > Make loose scan analysis work in sync with order by analysis. In the > case of duplicate > columns loose scan will not be applicable. This limitation will be > lifted in 10.0 by > removing duplicate columns. > >
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