Re: [HACKERS] Two questions about Postgres parser

On 2/27/17 10:37 AM, Tom Lane wrote:
>> 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?

FWIW, while working on a variant type I wished there was a way to 
preempt built-in type resolution when dealing with a particular type. I 
was specifically interested in function calls, which IIRC is handled by 
a single function and a helper. Exporting those two and providing a hook 
would have done the trick in my case.
-- 
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
855-TREBLE2 (855-873-2532)