As I know, IN sometimes invoke unmormal index.
On Thu, May 28, 2009 at 1:15 AM, Baron Schwartz ba...@xaprb.com wrote:
Simon,
On Wed, May 27, 2009 at 11:23 AM, Simon J Mudd sjm...@pobox.com wrote:
per...@elem.com (Perrin Harkins) writes:
On Wed, May 27, 2009 at 6:43 AM, Simon J Mudd sjm...@pobox.com wrote:
So is the format of the DELETE FROM .. WHERE ... IN ( ... ) clause I
propose valid and SHOULD the optimiser recognise this and be expected
to just find the 2 rows by searching on the primary key?
Not according to the docs:
http://dev.mysql.com/doc/refman/5.1/en/comparison-operators.html#function_in
I'm not sure that the reference makes anything clear. The statements
are wrote ARE valid SQL and even though containing mulitiple column
values ARE constants.
Problem is I'm finding it hard to find a definitive reference to
something
like this. I'll have to check my Joe Celko books to see if he mentions
ths.
Nothing's wrong with the SQL -- it's just that MySQL doesn't optimize
this type of query well.
See
http://code.openark.org/blog/mysql/mysql-not-being-able-to-utilize-a-compound-index
Regards
Baron
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