Date: Thu, 13 Oct 2022 15:34:50 -0400
From: Bruce Momjian <bruce@momjian.us>
To: matthias01123@gmail.com, pgsql-docs@lists.postgresql.org
Subject: Re: COALESCE could use some better examples
Message-ID: <Y0hoWkhgtl9fWsBn@momjian.us>
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On Thu, Oct 13, 2022 at 02:28:23PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/15/functions-conditional.html
> Description:
> 
> Regarding:
> https://www.postgresql.org/docs/current/functions-conditional.html
> 
> I ran into a situation where COALESCE was used like this
> 
> ```
> SELECT * FROM table WHERE COALESCE(col_1, col_2, col_3) >= 5
> ```
> 
> and didn't understand how it worked, and the examples don't really help
> because they only use COALESCE like
> 
> ```
> SELECT COALESCE(..)
> ```
> 
> I asked and answered a question on stackoverflow with a pretty good example
> of this, you could consider adding to your page.
> 
> Thank you :))
> 
> Stackoverflow question link:
> https://stackoverflow.com/questions/74057319/coalesce-in-postgresql-conditional-displaying-seemingly-undocumented-behavior

I read the Stackoverflow thread and it seems you thought a column name
in the function in a WHERE clause should span all the rows looking for
the first non-NULL row, and only if they are all NULL, go to th next
parameter.  All WHERE functions are row-based so I don't see how to
actually improve our doc text without making it more confusing.  Sorry.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Indecision is a decision.  Inaction is an action.  Mark Batterson