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
Is this really true?
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."