Queries to use subselects instead of inner joins

[samuraisam]

Query performance should be identical (since we use a 2nd indexed table for filtering) however the query will be more versatile. For example, DELETEs don't work with INNER JOIN, or any join for that matter, but do with sub queries.

This could be an option vs the default.

Also investigate to confirm performance claims (using EXPLAIN)

This could also be used to "combine" indexes. Right now we choose the biggest index and exclude all others. Obviously, the best performance will be achieved with the lowest number of indexes, but it will be possible.