René Fournier wrote:
Thanks! I will try this Monday. On a related note, does the 'temporary
table' approach (creating, locking, dropping) significantly slow down
queries? I haven't had to use them yet, and my application is somewhat
performance sensitive, so... just curious.
It's actually a *lot* faster if you put some effort into it. When you
use a sub-query, any indexes on the original fields inside the sub-query
are not used in the join further up ( ie the derived table has no
indexes on it ). So if you have a lot of data coming through in the
sub-query, it's very much worth it to create a temporary table *with*
*indexes* on fields you will be joining on. I was hoping MySQL would
support automatically indexing result fields inside a sub-query like
this, but apparently it's not on the cards :(
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