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

hi,

Thank you for your reply!

I’m wondering—since the parameter has already been specified as float8 in the PREPARE statement, why is it still necessary to convert it to float8 again during EXECUTE?

原始邮件


发件人：Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at&gt;
发件时间：2025年7月3日 20:23
收件人：798604270 <798604270(at)qq(dot)com&gt;, pgsql-bugs <pgsql-bugs(at)lists(dot)postgresql(dot)org&gt;
主题：Re: BUG #18976: -0.0 with float8 will be transformed to 0 inprepare statement but not in normal execution

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

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

EXECUTE&nbsp;prepare_query(-0.0::float8);

&nbsp;?column?&nbsp;
══════════
&nbsp;t
(1&nbsp;row)

Yours,
Laurenz&nbsp;Albe