On 12/12/2013 04:36 PM, Tom Lane wrote:
> BTW, on further thought, I'm afraid this is a bigger can of worms than
> it appears. The remarks above presume that the subquery is simple enough
> to be pulled up, which is the case in this example. It might not be too
> hard to make that case work. But what if the subquery *isn't* simple
> enough to be pulled up --- for instance, it includes grouping or
> aggregation? Then there's no way to unify its WHERE clause with the upper
> semijoin qual. At the very least, this breaks the uniqueify-then-do-a-
> plain-join implementation strategy for semijoins.
After having thought about it further, I think I understand.
> So I'm now thinking this patch isn't worth pursuing. Getting all the
> corner cases right would be a significant amount of work, and in the
> end it would only benefit strangely-written queries.
Originally it seemed to me that I just (luckily) found a new opportunity
for the existing infrastructure. To change the infrastructure because of
this small feature would be exactly the opposite. Thanks for having
taken a look at it.
// Antonin Houska (Tony)
