Re: slow Subquery

[Oleksandr Byelkin]

yes, for now IN subqueries is rewriting via EXISTS-like ones. You can see real executed subquery if issue following sequences of commands:
EXPLAIN EXTENDED <your select query>;
SHOW WARNINGS;

situation will be beter if you have index on L.LARGE because direct index lookup function will be used in IN subquery. But if LARGE is really large it do not help much. We plan optimisation of IN but as far you need result now, You'd better rewrite it with JOIN:

select SMALL.* from SMALL left join LARGE on (L=S) where L.L is not null

and test all 3 variants, then coose fastest one.