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* varchar value comparisons not working?
@ 2009-04-24 13:59 Shawn Tayler <stayler@washoecounty.us>
0 siblings, 2 replies; 3+ messages in thread
From: Shawn Tayler @ 2009-04-24 13:59 UTC (permalink / raw)
To: pgsql-sql
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?
--
Sincerely,
Shawn Tayler
Radio Network Administrator
Washoe County Regional Communications System
Telecommunications Division
Technology Services Department
County of Washoe
State of Nevada
Ofc (775)858-5952
Cell (775)771-4241
FAX (775)858-5960
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: varchar value comparisons not working?
@ 2009-04-24 14:32 Tom Lane <tgl@sss.pgh.pa.us>
parent: Shawn Tayler <stayler@washoecounty.us>
1 sibling, 0 replies; 3+ messages in thread
From: Tom Lane @ 2009-04-24 14:32 UTC (permalink / raw)
To: stayler@washoecounty.us; +Cc: pgsql-sql
Shawn Tayler <stayler@washoecounty.us> writes:
> 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)
Probably those "blank" values of slid are really NULLs. A NULL isn't
"equal to" something else, but it isn't "unequal" either. You could
use IS DISTINCT FROM instead of != in your second query.
regards, tom lane
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: varchar value comparisons not working?
@ 2009-04-27 08:53 Jasen Betts <jasen@xnet.co.nz>
parent: Shawn Tayler <stayler@washoecounty.us>
1 sibling, 0 replies; 3+ messages in thread
From: Jasen Betts @ 2009-04-27 08:53 UTC (permalink / raw)
To: pgsql-sql
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.
^ permalink raw reply [nested|flat] 3+ messages in thread
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2009-04-24 13:59 varchar value comparisons not working? Shawn Tayler <stayler@washoecounty.us>
2009-04-24 14:32 ` Tom Lane <tgl@sss.pgh.pa.us>
2009-04-27 08:53 ` Jasen Betts <jasen@xnet.co.nz>
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