Re: Two questions about Postgres parser

Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru> writes:
> 1. Moving-aggregate implementation should return the same type as plain
> implementation. Yes, in most cases it is hard to find arguments why them
> should return different types. But it is not true for vectorized
> operations...

I can't see a reason why we would want to go there. And if your design
for vectorized operations requires different user-visible semantics than
for the same operation non-vectorized, don't you have a problem anyway?

> 2. Implicit user defined type casts are not applied for COALESCE operator:

That has nothing to do with whether the cast is user-defined. It has to
do with not wanting to automatically unify types across type-category
boundaries (in this case, numeric vs. composite categories). That's per
step 4 here:

https://www.postgresql.org/docs/devel/static/typeconv-union-case.html

and it's not an easy thing to get rid of because if you're considering
more than one type category then the heuristic about preferring "preferred
types" breaks down --- how do you know which category's preferred type to
prefer?

regards, tom lane