To: pgsql-sql@postgresql.org
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From: Jasen Betts <jasen@xnet.co.nz>
Newsgroups: gmane.comp.db.postgresql.sql
Subject: Re: varchar value comparisons not working?
Date: 27 Apr 2009 08:53:49 GMT
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On 2009-04-24, Shawn Tayler <stayler@washoecounty.us> wrote:
> Hello,
>
> I'm doing a quick comparison between a couple tables, trying to cleanup
> some inconsistencies, and what should be a simple check between 2 tables
> doesn't seem to be working.  psql is 8.3.7 and server is 8.2.13.
>
> I run the following:
>
> select sfd.lid as sflid,sd.lid as slid,sfd.serial from sfd,shawns_data
> sd where sfd.serial = sd.serial_number order by sfd.lid; 
>
> the lid columns in both tables should be identical, but as you see in
> this sample, they do differ:
>
>  sflid | slid  |  serial  
> -------+-------+----------
>  14056 | 14056 | 9614583
>  14057 |       | 9614984
>  14058 | 14058 | 9614737
>  14059 | 14059 | 9614579
>  14060 |       | 9614827
>  14061 | 14061 | 9614726
>  14062 | 14062 | 9614966
>  14063 | 14063 | 9615079
>
> So running this query:
>
> select count(*) from sfd,shawns_data sd where sfd.serial = sd.serial_number and sfd.lid != sd.lid; 
>
> I should show some rows that do not match, at least 2 (there are more than shown).  
>
> But instead I get this:
>
>  count 
> -------
>      0
> (1 row)
>
>
> What am I doing wrong?

expecting NULL values not-equal something.


select count(*) 
  from sfd,shawns_data sd 
  where sfd.serial = sd.serial_number 
  and COALESCE( sfd.lid != sd.lid, TRUE )
  

the above include rows where both are NULL, if that's undesirable 
they must be explicitly excluded.