Re: BUG #18429: Inconsistent results on similar queries with join lateral

I suspected a rounding issue at some point, but using floor didn't helped.
Displaying the values of `c2.t` shows more:
```
with c2 as (
  select arrayd.ad d, coalesce(c.t, 0) t
    from unnest(ARRAY[4]) as arrayd(ad)
    left join lateral (
      select wt t from weird.t
        where wd = arrayd.ad
        order by wt desc limit 1
    ) c on true
)
select c2.t, c2.d from c2
  where (14 - c2.t) / c2.d = (12 - c2.t) / c2.d;

 t | d
---+---
 0 | 4
(1 row)

with c2 as (
  select arrayd.ad d, coalesce(c.t, 0) t
    from unnest(ARRAY[4]) as arrayd(ad)
    left join lateral (
      select wt t from weird.t
        where wd = arrayd.ad
        order by wt desc limit 1
    ) c on true
)
select c2.t, c2.d from c2
  where true;

 t | d
---+---
 6 | 4
(1 row)
```

The only difference is the where clause, and it changes the returned value of `c2.t`.
If `c2.t = 0`, the where condition is true with proper integer rounding/truncation, which explains the result from Q1.
________________________________
From: David G. Johnston <david.g.johnston@gmail.com>
Sent: Friday, April 12, 2024 15:52
To: Benoit Ryder <b.ryder@ateme.com>; pgsql-bugs@lists.postgresql.org <pgsql-bugs@lists.postgresql.org>
Subject: Re: BUG #18429: Inconsistent results on similar queries with join lateral

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On Friday, April 12, 2024, PG Bug reporting form <noreply@postgresql.org<mailto:noreply@postgresql.org>> wrote:
The following bug has been logged on the website:

Bug reference:      18429
Logged by:          Benoît Ryder
Email address:      b.ryder@ateme.com<mailto:b.ryder@ateme.com>
PostgreSQL version: 15.6
Operating system:   Debian
Description:

-- `where` clause should return false: (14 - 6) / 4 = (12 - 6) / 4 → false
select 1 from c2 where (14 - c2.t) / c2.d = (12 - c2.t) / c2.

You are doing integer division here and the right hand side equals, 1.5; I suppose something may have used to round that up to the integer 2 which would make both sides equals but now (v16) rounds it down (or more accurately truncates it) to 1.

David J.