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." > > > > > John Daisley Email: john.dais...@butterflysystems.co.uk Mobile: +44 (0)7812 451238 MySQL Certified Database Administrator (CMDBA) MySQL Certified Developer (CMDEV) MySQL Certified Associate (CMA) Comptia A+ Certified Professional IT Technician ------- Life's journey is not to arrive at the grave safely in a well preserved body, but rather to slide in sideways, thoroughly used up, totally worn out and screaming "Wow! what a ride!"
