Hi all,
I am wondering if anyone have any knowledge if there is speed difference between joins (inner | outer | left | right) and subqueries. Would I actually gain preformance using subqueries (new since 4.1) against using the "old" joins?
Would be interesting to hear comments on this matter, and also a detailed explanation on which is to prefer and why.
Subquery optimizer is still is a very early stage in 4.1. Much more often than not, a carefully crafted join, union, or a sequence of queries using a temporary table will be faster. In fact, I wonder if it is even possible to write a machine subquery optimizer that will outperform a good human "optimizer" that re-writes them into something better digestible. Kind of like no super-smart JIT will ever beat a good C programmer on execution speed, although it might help with the development time.
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