Thread

Re: Some optimizations for COALESCE expressions during constant folding

David Rowley <dgrowleyml@gmail.com> — 2025-11-25T13:10:45Z

On Tue, 25 Nov 2025 at 23:51, Richard Guo <guofenglinux@gmail.com> wrote:
> (I'm wondering whether it'd be better to consolidate the
> non-null check for Const, Var, and CoalesceExpr into one helper
> function to simplify the code in eval_const_expressions.)

uhh, of course it is. That's what I did in [1] for Consts and expand
expr_is_nonnullable() to support COALESCE exprs then modify
eval_const_expressions_mutator() to use that rather than using
var_is_nonnullable(). That way we'll not need to modify the constant
folding code every time we think of something new that we can prove
can't be NULL.

David

[1] https://www.postgresql.org/message-id/attachment/184166/v3-0001-Have-the-planner-replace-COUNT-ANY-with-COUNT-whe.patch