> Den 20. apr. 2016 kl. 20.15 skrev Sergei Golubchik <s...@mariadb.org>: > > On Apr 20, Erik Cederstrand wrote: >> >> CREATE TABLE `t1` ( `i` int(11) NOT NULL, `j` int(11) NOT NULL, `l` >> int(11) NOT NULL, `m` int(11) DEFAULT NULL, PRIMARY KEY >> (`i`,`j`,`l`)); >> >> CREATE TABLE `t2` ( `i` int(11) NOT NULL, `k` int(11) DEFAULT NULL, >> PRIMARY KEY (`i`)) ENGINE=InnoDB DEFAULT CHARSET=utf8; >> >> The problematic query is this: >> SELECT DISTINCT t2.i, t2.k, t1.j, t1.l, t1.m FROM t2 LEFT JOIN t1 >> ON t2.i=t1.i WHERE t2.k < 123; >> >> The query is slow because the DISTINCT clause forces the query to use >> a temporary table. Removing DISTINCT makes the query 100x faster. >> ... >> it could also be argued that MariaDB should be smart enough to detect >> that the DISTINCT is unnecessary and ignore it (should I create a bug >> report for that?). > > Yes, please, do report it! On the first glance this looks like a rather > simple optimization.
Thanks. Reported as https://jira.mariadb.org/browse/MDEV-9964 Erik
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