Mischa Sandberg <mischa@ca.sophos.com> writes:
> can PG see that a join on an grouped-by field
> can be pushed down into the query as an indexable filter?
No. The GROUP BY serves as a partial optimization fence. If you're
concerned about the speed of this query, I recommend making a different
view in which 'message' is joined inside the GROUP BY.
regards, tom lane