Re: varchar value comparisons not working?

On 2009-04-24, Shawn Tayler <stayler(at)washoecounty(dot)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.