Re: Optimizing nested ConvertRowtypeExpr execution

On Mon, Apr 9, 2018 at 3:49 PM, Kyotaro HORIGUCHI
<horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>
> I don't think it is not only on constatns. With the patch,
> non-constants are .. getting a rather strange conversion.
>
>
>> =# explain verbose select (a, b, c)::t1p1p1::t1p1::t1 from (select i, i * 2, i * 3 from generate_series(0, 10) i) x(a, b, c);
>> QUERY PLAN
>> -------------------------------------------------------------------------
> ...
>> Output: (ROW(i.i, (i.i * 2), (i.i * 3))::t1p1p1)::t1
>
> Conversions between scalar values cannot be assumed safely
> composed each other for general inputs but it is known to be safe
> for the ConvertRowtypeExpr case.. I think.

I am not able to parse this statement.

What output do you see without the patch?

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company