SMF 2.0.9 and 1.1.20 have been released! Please update. Read more.
Repair TABLE smf_sessions;
I guess you can change that by hacking into the database, like this: http://help.electricfunction.com/kb/caribou-cms/how-to-hide-database-errors-from-your-website-visitors
That's not for MySQL as a whole, it's for a specific app.
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