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* select only 1 pair
@ 2022-10-24 14:44 Shaozhong SHI <shishaozhong@gmail.com>
0 siblings, 4 replies; 6+ messages in thread
From: Shaozhong SHI @ 2022-10-24 14:44 UTC (permalink / raw)
To: pgsql-sql <pgsql-sql@lists.postgresql.org>
There are pair ids. Each pair is repeated.
id1 id2
1 2
2 1
3 4
4 3
How to only select 1 unique pair for each?
Regards,
David
^ permalink raw reply [nested|flat] 6+ messages in thread
* RE: select only 1 pair
@ 2022-10-24 14:59 Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
parent: Shaozhong SHI <shishaozhong@gmail.com>
3 siblings, 0 replies; 6+ messages in thread
From: Voillequin, Jean-Marc @ 2022-10-24 14:59 UTC (permalink / raw)
To: Shaozhong SHI <shishaozhong@gmail.com>; pgsql-sql <pgsql-sql@lists.postgresql.org>
select id1,id2 from your_table where id2>=id1
union
select id2,id1 from your_table where id2<id1;
should work
From: Shaozhong SHI <shishaozhong@gmail.com>
Sent: Monday, October 24, 2022 4:44 PM
To: pgsql-sql <pgsql-sql@lists.postgresql.org>
Subject: select only 1 pair
There are pair ids. Each pair is repeated. id1 id2 1 2 2 1 3 4 4 3 How to only select 1 unique pair for each? Regards, David
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There are pair ids. Each pair is repeated.
id1 id2
1 2
2 1
3 4
4 3
How to only select 1 unique pair for each?
Regards,
David
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^ permalink raw reply [nested|flat] 6+ messages in thread
* Re: select only 1 pair
@ 2022-10-24 15:01 William Alves Da Silva <william_silva@unochapeco.edu.br>
parent: Shaozhong SHI <shishaozhong@gmail.com>
3 siblings, 1 reply; 6+ messages in thread
From: William Alves Da Silva @ 2022-10-24 15:01 UTC (permalink / raw)
To: pgsql-sql <pgsql-sql@lists.postgresql.org>; Shaozhong SHI <shishaozhong@gmail.com>
Hello David,
Try this.
This is an exemple of your table.
SELECT *
FROM (VALUES (1, 2), (2, 1), (3, 4), (4, 1)) t (id1, id2)
id1 |id2 |
------+------+
1| 2|
2| 1|
3| 4|
4| 1|
I think that is what you need
SELECT DISTINCT LEAST(id1, id2) AS id1, GREATEST(id1, id2) AS id2
FROM (VALUES (1, 2), (2, 1), (3, 4), (4, 3)) t (id1, id2)
id1 |id2 |
------+------+
1| 2|
3| 4|
Regards,
William Alves
On 24 Oct 2022 11:44 -0300, Shaozhong SHI <shishaozhong@gmail.com>, wrote:
> There are pair ids. Each pair is repeated.
>
> id1 id2
> 1 2
> 2 1
> 3 4
> 4 3
>
> How to only select 1 unique pair for each?
>
> Regards,
>
> David
^ permalink raw reply [nested|flat] 6+ messages in thread
* Re: select only 1 pair
@ 2022-10-24 15:01 Frank Streitzig <fstreitzig@gmx.net>
parent: Shaozhong SHI <shishaozhong@gmail.com>
3 siblings, 0 replies; 6+ messages in thread
From: Frank Streitzig @ 2022-10-24 15:01 UTC (permalink / raw)
To: Shaozhong SHI <shishaozhong@gmail.com>; +Cc: pgsql-sql <pgsql-sql@lists.postgresql.org>
Am Mon, Oct 24, 2022 at 03:44:03PM +0100 schrieb Shaozhong SHI:
> There are pair ids. Each pair is repeated.
>
> id1 id2
> 1 2
> 2 1
> 3 4
> 4 3
>
> How to only select 1 unique pair for each?
>
> Regards,
> David
Hello,
if just 2 id's then sort with min and max comparing.
Example:
with data (id1, id2) as (
values (1,2), (2,1), (3,4), (4,3)
)
select case when id1 <= id2 then id1 else id2 end as idmin
, case when not id1 <= id2 then id1 else id2 end as idmin
from data
group by 1, 2
;
Best regards,
Frank
^ permalink raw reply [nested|flat] 6+ messages in thread
* Re: select only 1 pair
@ 2022-10-24 15:08 Thomas Kellerer <shammat@gmx.net>
parent: Shaozhong SHI <shishaozhong@gmail.com>
3 siblings, 0 replies; 6+ messages in thread
From: Thomas Kellerer @ 2022-10-24 15:08 UTC (permalink / raw)
To: pgsql-sql@lists.postgresql.org
Shaozhong SHI schrieb am 24.10.2022 um 16:44:
> There are pair ids. Each pair is repeated.
>
> id1 id2
> 1 2
> 2 1
> 3 4
> 4 3
>
> How to only select 1 unique pair for each?
select distinct least(id1,id2), greatest(id1,id2)
from the_table
^ permalink raw reply [nested|flat] 6+ messages in thread
* Re: select only 1 pair
@ 2022-10-24 15:57 Steve Midgley <science@misuse.org>
parent: William Alves Da Silva <william_silva@unochapeco.edu.br>
0 siblings, 0 replies; 6+ messages in thread
From: Steve Midgley @ 2022-10-24 15:57 UTC (permalink / raw)
To: William Alves Da Silva <william_silva@unochapeco.edu.br>; +Cc: pgsql-sql <pgsql-sql@lists.postgresql.org>; Shaozhong SHI <shishaozhong@gmail.com>
On Mon, Oct 24, 2022 at 8:02 AM William Alves Da Silva <
william_silva@unochapeco.edu.br> wrote:
> Hello David,
>
> Try this.
>
> This is an exemple of your table.
> *SELECT* *
> *FROM* (*VALUES* (1, 2), (2, 1), (3, 4), (4, 1)) t (id1, id2)
>
> id1 |id2 |
> ------+------+
> 1| 2|
> 2| 1|
> 3| 4|
> 4| 1|
>
>
> I think that is what you need
> *SELECT* *DISTINCT* *LEAST*(id1, id2) *AS* id1, *GREATEST*(id1, id2) *AS*
> id2
> *FROM* (*VALUES* (1, 2), (2, 1), (3, 4), (4, 3)) t (id1, id2)
>
> id1 |id2 |
> ------+------+
> 1| 2|
> 3| 4|
>
>
>
I'll let OP clarify, but in your dataset example (not the same as
original), shouldn't "4, 1" be found also. It's a unique pair (whereas
"1,2" and "2,1" are repeating when sorted low/high). Which makes me think
that merging the two columns into an array, sorting the array, and then
squasing duplicates would do the job? Maybe there's an easier way, but from
what I can see of the original requirements, your dataset should return the
following?
1 | 2
3 | 4
4 | 1
Steve
^ permalink raw reply [nested|flat] 6+ messages in thread
end of thread, other threads:[~2022-10-24 15:57 UTC | newest]
Thread overview: 6+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2022-10-24 14:44 select only 1 pair Shaozhong SHI <shishaozhong@gmail.com>
2022-10-24 14:59 ` Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
2022-10-24 15:01 ` William Alves Da Silva <william_silva@unochapeco.edu.br>
2022-10-24 15:57 ` Steve Midgley <science@misuse.org>
2022-10-24 15:01 ` Frank Streitzig <fstreitzig@gmx.net>
2022-10-24 15:08 ` Thomas Kellerer <shammat@gmx.net>
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