Re: [HACKERS] Two questions about Postgres parser

Konstantin Knizhnik <k.knizhnik@postgrespro.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