Hello,
I recently encountered a case where partial indexes were surprisingly not being used. The issue is that predtest doesn't understand how boolean values and IS <boolean> expressions relate.
For example if I have:
create table foo(i int, bar boolean);
create index on foo(i) where bar is true;
then this query:
select * from foo where i = 1 and bar;
doesn't use the partial index.
Attached is a patch that solves that issue. It also teaches predtest about quite a few more cases involving BooleanTest expressions (e.g., how they relate to NullTest expressions). One thing I could imagine being an objection is that not all of these warrant cycles in planning. If that turns out to be the case there's not a particularly clear line in my mind about where to draw that line.
As noted in a TODO in the patch itself, I think it may be worth refactoring the test_predtest module to run the "x, y" case as well as the "y, x" case with a single call so as to eliminate a lot of repetition in clause/expression test cases. If reviewers agree that's desirable, then I could do that as a precursor.
Regards,
James Coleman
