Thanks Michael.
I'll give some join alternatives a shot first... but, that's cool.
What about OFFSET 0 makes this approach work? I'm thinking the OFFSET 0 create an optimization barrier that prevents the planner from collapsing that sub-query into the top query, and enforces ordering in the query?
I appreciate your thoughts, thank-you very much for the feedback.
Mathieu
On Wed, Aug 21, 2019 at 12:08 PM Michael Lewis <mlewis@xxxxxxxxxxx> wrote:
If those conditions that are throwing off the stats are expected to be minimally impactful/filtering few rows, then you can use the one tried-and-true optimizer hint (aside from materialized CTEs, stylized indexes, etc) --- OFFSET 0 at the end of a sub-query.SELECT * FROM ( [your existing query without the sub-selects that are complicated and produce bad estimates] OFFSET 0 ) WHERE [your other conditions that don't produce good estimates]If there is correlation between field1 and field2, you might also look at CREATE STATISTICS assuming you are on PG 10 or 11.Before I do any of that, I would try LEFT JOIN for Table3 and Table4 then use the where conditon "AND 2 = COALESCE( Table3.Status, Table4.Status" and see if the optimizer likes that option better.
