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Optimizer : wrong index choice, leading to strong performances issues

Hi,

I'm recreating in JIRA a Launchpad bug opened 2 years ago (https://bugs.launchpad.net/maria/+bug/639949), which is itself a follow up of a really annoying MySQL optimiser bug opened 4 years ago (http://bugs.mysql.com/bug.php?id=36817)

To summarize, there are several simple cases where MySQL optimiser doesn't select the right index. This entails strong performance issues (especially when filesorting is involved), and force the developers to hack their applications, using USE INDEX (when it's possible...).

Hoping someone finally takes a look at this serious issue...
Actually it could also help some of my customers to switch to mariadb, because they are also a little bit tired to put USE INDEX everywhere in there code

Thanks and regards,
Jocelyn Fournier

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