From: Gary Stainburn <gary.stainburn@ringways.co.uk>
Organization: Ringways Garages Ltd
To: pgsql-sql@lists.postgresql.org
Subject: Re: select where not in () fails
Date: Fri, 21 Sep 2018 16:20:16 +0100
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Cc: Pavel Stehule <pavel.stehule@gmail.com>
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On Friday 21 September 2018 16:11:17 Pavel Stehule wrote:
>  maybe some value emp_u_id from employees is NULL. It is expected behave
>
> http://blog.9minutesnooze.com/sql-not-in-subquery-null/
>
> Regards
>
> Pavel


Thanks for this. 

As I said in my description, some values will be NULL. I just thought that 
these would not be included in the select. I did not think that it would stop 
the subselect from working

users=# select count(u_id) from users where u_id not in (select distinct 
emp_u_id from employees where emp_u_id is not null);
 count 
-------
   393
(1 row)

users=#