Apparently the latest version of MySQL has solved this problem: 
http://www.xaprb.com/blog/2006/06/28/why-large-in-clauses-are-problematic/

But I am running PostgreSQL v8.3 and am observing generally that SELECT ... 
WHERE ... IN (a, b, c, ...) is much slower than SELECT ... INNER JOIN (SELECT a 
UNION ALL SELECT b UNION ALL SELECT c ...)

Why doesn't the optimizer automatically transform IN clauses to INNER JOINs in 
this fashion?





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