Le mercredi 26 août 2009 à 07:25 -0700, David Metzler a écrit : > A good decision on wether to use multi-column indexes will take into > account the cardinality of the data. Sometimes a multi-column index > is simply the right answer, particularly if the values in the first > column of the index do not limit the rows sufficiently. Also in > where exists clauses the rdbms will not even load the row if the > primary key is the composite index, but it will have to. Indexes > are > best thought of like caches, You use the right caching mechanism > for > the job, and you only do it when you can demonstrate performance > improvement.
Thanks David, I added this comment on the page, which is a perfect summary. Kind regards, Jean-Michel
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