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@qq.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