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From: Tom Lane <[email protected]>
To: Tomasz Szypowski <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: View performance with implicit cast
Date: Sat, 04 Jan 2025 13:37:29 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <DU0PR04MB94192D3922E05C8E0A18F5F399142@DU0PR04MB9419.eurprd04.prod.outlook.com>
References: <DU0PR04MB94192D3922E05C8E0A18F5F399142@DU0PR04MB9419.eurprd04.prod.outlook.com>

Tomasz Szypowski <[email protected]> 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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