On Tue, 2009-07-21 at 19:42 +0200, Morten Primdahl wrote:
> On Jul 21, 2009, at 3:27 PM, Johnny Withers wrote:
> > MySQL is unable to use your index when you use IN and/or OR on yoru
> > column.
> Is this really true?
No its not true! Try running OPTIMIZE TABLE on the affected table, then
run the query again and see if the other index is used!
> I'm reading "High Performance MySQL 2nd ed." these days and
> specifically got the impression that using IN will allow usage of the
> index. The below quote is from the book, and the "multiple equality
> condition" refers to an IN (...) expression.
> "... we draw a distinction between ranges of values and multiple
> equality conditions.The second query is a multiple equality condition,
> in our terminology. We’re not just being picky: these two kinds of
> index accesses perform differently. The range condition makes MySQL
> ignore any further columns in the index, but the multiple equality
> condition doesn’t have that limitation."
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