Re: Improve documentation for current_setting function

On Wed, Feb 20, 2019 at 12:59:45PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/11/functions-admin.html
> Description:
> 
> Hi.
> 
> Doc is not clear about what is returned if current_setting(
> 'app.not_existent', true ) is called.
> 
> Does it return empty string '', because return type is 'text' or it return
> NULL, because 'app.not_existent' does not exist

Testing shows:

	SELECT current_setting('asdf', true);
	 current_setting
	-----------------
	
	
	\pset null (null)
	
	SELECT current_setting('asdf', true);
	 current_setting
	-----------------
-->	 (null)

How do you like the attached patch, which clarifies this?

-- 
  Bruce Momjian  <[email protected]>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
new file mode 100644
index 86ff4e5..f638c6d
*** a/doc/src/sgml/func.sgml
--- b/doc/src/sgml/func.sgml
*************** SELECT current_setting('datestyle');
*** 18722,18728 ****
      If there is no setting named <parameter>setting_name</parameter>,
      <function>current_setting</function> throws an error
      unless <parameter>missing_ok</parameter> is supplied and is
!     <literal>true</literal>.
     </para>
  
     <para>
--- 18722,18729 ----
      If there is no setting named <parameter>setting_name</parameter>,
      <function>current_setting</function> throws an error
      unless <parameter>missing_ok</parameter> is supplied and is
!     <literal>true</literal>, in which case a missing parameter returns
!     NULL.
     </para>
  
     <para>