Re: [BUGS] Failure to coerce unknown type to specific type

On 4/23/15 5:07 AM, Kyotaro HORIGUCHI wrote:
> This is because parsing of UNION immediately converts constants
> of unknown type in the UNION's both arms to text so the top level
> select won't be bothered by this problem. But the problematic
> query doesn't have appropriate timing to do that until the
> function I patched.

FWIW, I think that's more accidental than anything.

I'm no expert in our casting and type handling code but I spent a lot of 
time stuck in it while working on the variant type, and it seems very 
scattered. There's stuff in the actual casting code, there's some stuff 
in other parts of parse/plan, there's stuff in individual types (array 
and record at least).

Some stuff is handled by casting; some stuff is handled by mangling the 
parse tree.

Something else I noticed is we're not consistent with handling typmod 
either. I don't remember the exact example I found, but there's cases 
involving casting of constants where we ignore it (I don't think it was 
as simple as SELECT 1::int::variant(...), but it was something like that).

I don't know how much of this is just historical and how much is 
intentional, but it'd be nice if we could consolidate it more.
-- 
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com