On Wed, 16 Jan 2019 at 03:33, James Coleman <jtc...@gmail.com> wrote: > > 2. I was also staring predicate_implied_by_simple_clause() a bit at > > the use of clause_is_strict_for() to ensure that the IS NOT NULL's > > operand matches the ScalarArrayOpExpr left operand. Since > > clause_is_strict_for() = "Can we prove that "clause" returns NULL if > > "subexpr" does?", in this case, your clause is the ScalarArrayOpExpr's > > left operand and subexpr is the IS NOT NULL's operand. This means > > that a partial index with "WHERE a IS NOT NULL" should also be fine to > > use for WHERE strict_func(a) IN (1,2,..., 101); since strict_func(a) > > must be NULL if a is NULL. Also also works for WHERE a+a > > IN(1,2,...,101); I wonder if it's worth adding a test for that, or > > even just modify one of the existing tests to ensure you get the same > > result from it. Perhaps it's worth an additional test to ensure that x > > IN(1,2,...,101) does not imply x+x IS NOT NULL and maybe that x+x IS > > NULL does not refute x IN(1,2,...,101), as a strict function is free > > to return NULL even if it's input are not NULL. > > Are you suggesting a different test than clause_is_strict_for to > verify the saop LHS is the same as the null test's arg? I suppose we > could use "equal()" instead?
I wasn't suggesting any code changes. I just thought the code was sufficiently hard to understand to warrant some additional tests that ensure we don't assume that if the int4 column x is not null that also x+x is not null. Only the reverse can be implied since int4pl is strict. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
