26 Aug
2009
26 Aug
'09
4:47 p.m.
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