On Wed, Jun 30, 2021 at 12:21 PM Andrey Lepikhov <a.lepik...@postgrespro.ru> wrote:
> On 12/3/21 12:05, Hywel Carver wrote: > > I've built and tested this, and it seems to function correctly to me. > One question I have is whether the added "IS NOT NULL" filters can be > omitted when they're unnecessary. Some of the resulting plans included an > "IS NOT NULL" filter on a non-nullable column. To be clear, this is still > an improvement (to me) without that. I think, here we could ask more general question: do we want to remove a > 'IS NOT NULL' clause from the clause list if the rest of the list > implicitly implies it? My suggestion was not to remove it, but to avoid adding it in the first place. When your optimisation has found a join on a group of columns under a uniqueness constraint, you would do something like this (forgive the pseudo-code) foreach(column, join_clause) { if(column.nullable) { // This condition is what I'm suggesting is added add_null_test(column, IS_NOT_NULL); } } But it may be that that's not possible or practical at this point in the code.