Laurenz Albe <laurenz.albe@xxxxxxxxxxx> writes: > On Sun, 2022-09-18 at 18:24 +0300, Евгений Плискин wrote: >> So why not use this index for this query? > Because the conditions are different: > SELECT NULL = TRUE, NULL IS TRUE; > ?column? │ ?column? > ══════════╪══════════ > │ f > (1 row) > The first result is NULL. Nonetheless, indxpath.c knows it can transform between "bool = true" and "bool IS TRUE" for the purpose of making an index search qualification, so it seems a bit odd that we fail to do the equivalent transformation when attempting to prove an index predicate. It'd be possible to improve this by adding some proof rules to predicate_implied_by_simple_clause: I think both "x => x IS TRUE" and the converse would be valid per the proof requirements, and if you wanted to gild the lily it'd likely be possible to handle some related cases like "x => x IS NOT FALSE". Whether it's worth the cycles isn't too clear to me, but we could argue about that if somebody submitted a patch. regards, tom lane
