Hello Philip, I'd like to get the tree at lp:~maria-captains/maria/5.3-subqueries-mwl90 tested for Duplicate Elimination with outer+semi-join processing. I'm interested in crashes, as well as wrong query result bugs. The code path that needs to be tested is selected with this @@optimizer_switch setting: semijoin=on,materialization=off,firstmatch=off,loosescan=off this set of switches disables all semi-join subquery strategies except DuplicateElimination, so you should have no problem with hitting the If you also set "semijoin=off" then you get the execution path that we assume will always produce correct results. Query pattern SELECT .... FROM complex_join WHERE top_where AND (SELECT ... FROM complex_join WHERE ...) where - subqueries must be "mergeable semi-joins": = no aggregates, unions, or ORDER BYs - both correlated and ucorrelated subqueries are OK. - complex_join is arbitrary join structure (comma join, "t1 JOIN t2", various kinds of outer joins - everything should work) - multiple sibling subqueries, as well as nested subqueries are covered by what you're testing. EXPLAIN - Should have id=='1' && select_type='PRIMARY' on all lines. - Should use Start Temporary/End temporary. BR Sergey -- Sergey Petrunia, Software Developer Monty Program AB, http://askmonty.org Blog: http://s.petrunia.net/blog