Re: BUG #18976: -0.0 with float8 will be transformed to 0 in prepare statement but not in normal execution

On Thu, 2025-07-03 at 03:03 +0000, PG Bug reporting form wrote:
> The following bug has been logged on the website:
>
> Bug reference: 18976
> Logged by: Chi Zhang
> Email address: 798604270(at)qq(dot)com
> PostgreSQL version: 18beta1
> Operating system: Ubuntu 24.04 and docker
> Description:
>
> The value -0.0 with float8 is transformed to 0 in prepared statements but
> remains -0 in normal execution. Although 0 and -0 are numerically equal,
> this discrepancy can lead to subtle bugs in certain cases—for example, when
> the value is cast to a VARCHAR, as illustrated below.
>
> PREPARE prepare_query (float8) AS SELECT CAST($1 AS VARCHAR) =
> CAST(-0.0::float8 AS VARCHAR);
> EXECUTE prepare_query(-0.0); -- f

That's not a bug, but a pilot error. If you feed a "float8", the result ist TRUE:

EXECUTE prepare_query(-0.0::float8);

?column?
══════════
t
(1 row)

Yours,
Laurenz Albe