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Re: Philip please test: Duplicate Elimination for outer joins + semijoins



I have tested your tree as much as I could and filed a few bugs. I can only resume testing after those bugs are fixed. Preferably *all* of them, this will also prevent the bugs from getting so stale that they are no longer repeatable.

For a list of all the dimensions that are being tested and the complexity in each direction, see:


I could not fully test the following 2 things:
- nested subqueries, blocked due to 802979
- views and derived tables, blocked due to crashes


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.

Yes, I am doing exactly that.

Query pattern

 SELECT .... FROM complex_join
   top_where AND (SELECT ... FROM complex_join WHERE ...)

Yes, this pattern is covered

- 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)

We do joins of up to 3 tables in the inner and the outer query. Both inner and outer joins, both comma joins and joins with ON .

- multiple sibling subqueries, as well as nested subqueries are covered by
  what you're testing.

As noted above, nested subqueries are blocked. Multiple subqueries per query are tested.

- Should have id=='1' && select_type='PRIMARY' on all lines.
- Should use Start Temporary/End temporary.

Yes I am able to hit this EXPLAIN reliably.