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From: David G. Johnston <[email protected]>
To: Damian Lukowski <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: BUG #19428: Lazy evaluation of type checking in CASE in SQL functions including subqueries no longer works in 18
Date: Thu, 12 Mar 2026 05:40:12 -0700
Message-ID: <CAKFQuwZN90TwSJJ=1zu88pkkC1e5c_wKDMsO5_849uwa2zDmhQ@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>

On Thursday, March 12, 2026, Damian Lukowski <[email protected]> wrote:

> We have never promised to avoid constant-folding within the
> subexpressions of a CASE [1].  So it was pure accident that
> this example worked before, and I don't think it's a bug that
> it doesn't work now.
>
> For a better understanding, which one is the constant that is being
> folded? I have found several articles explaining constant folding but their
> examples are obvious, e.g. `7 + 1` can be folded to `8` [1, 2], or `1 = 1`
> can be folded to `TRUE` [3].
>
> However, I have not found any articles that resemble this case. Aren't
> `arg` and `$1` variables? Where is the boundary between constants and
> non-constants?
>
The system is capable of postponing planning until (or performing
replanning) after parameter values are known, in which the values they are
given are constants.

David J.

>

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  Subject: Re: BUG #19428: Lazy evaluation of type checking in CASE in SQL functions including subqueries no longer works in 18
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