| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Tomasz Szypowski <tomasz(dot)szypowski(at)asseco(dot)pl> |
| Cc: | "pgsql-sql(at)lists(dot)postgresql(dot)org" <pgsql-sql(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: View performance with implicit cast |
| Date: | 2025-01-04 18:37:29 |
| Message-ID: | 640397.1736015849@sss.pgh.pa.us |
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| Lists: | pgsql-sql |
Tomasz Szypowski <tomasz(dot)szypowski(at)asseco(dot)pl> writes:
> I have got an example, in which PostgreSQL could speed up:
The reason why the first version of the view doesn't behave well
is that it's not optimized into an "append relation", because
is_simple_union_all() doesn't think that's safe:
/*
* is_simple_union_all
* Check a subquery to see if it's a simple UNION ALL.
*
* We require all the setops to be UNION ALL (no mixing) and there can't be
* any datatype coercions involved, ie, all the leaf queries must emit the
* same datatypes.
*/
Perhaps this could be improved, but it's a lot easier just to add
the cast yourself.
regards, tom lane
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