Re: Partition prune with stable Expr

Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> writes:
> Well, that's very interesting. Specific to my user case,
> SELECT * FROM p WHERE pkey = to_date('2018-12-13', 'yyyy-mm-dd)';
> p has 1500+ partitions and planning takes lots of time, which is so same
> with SELECT * FROM p WHERE pkey = '2018-12-13', however the planning
> time difference is so huge, that doesn't make sense in human view. Can
> we do something for that? to_date(text, text) should be a "immutable"
> function IMO. Does that have a semantic issue or other issues?

Yeah. It depends on the lc_time setting, and possibly also the timezone
GUC. (Admittedly, common values of the format string would not have
any lc_time dependency, but the immutability property is not fine-grained
enough to recognize that.)

regards, tom lane