Nicolas Adenis-Lamarre <nicolas.adenis.lamarre@gmail.com> writes: > - detect anti join on "a left join b where x is null" where x is a non null > var b (b being a rte) > this is the object of the attached patched.
This is a perfectly reasonable thing to do, especially now that we've built out some infrastructure that would help. It doesn't look like your patch is using that though. Take a look at commits 904f6a593 and e2debb643.
Yes, after commits 904f6a593 and e2debb643, we have some infrastructure to use.
I provided a patch to implement this reduction using these infrastructure codes.
Please check the attached patch.
BTW, it is not a good look for even a draft patch to not bother updating adjacent comments that it falsifies, such as this in reduce_outer_joins_pass2:
* See if we can reduce JOIN_LEFT to JOIN_ANTI. This is the case if * the join's own quals are strict for any var that was forced null by * higher qual levels. NOTE: there are other ways that we could * detect an anti-join, in particular if we were to check whether Vars * coming from the RHS must be non-null because of table constraints. * That seems complicated and expensive though (in particular, one * would have to be wary of lower outer joins). For the moment this * seems sufficient.
In the long run, the comments are as important as the code, if not even more so. Keeping them accurate is not optional.
I updated the comments in the attached patch as well.
And I test the regression in the src, all tests pass.
