| From: | Frank Streitzig <fstreitzig(at)gmx(dot)net> |
|---|---|
| To: | Shaozhong SHI <shishaozhong(at)gmail(dot)com> |
| Cc: | pgsql-sql <pgsql-sql(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: select only 1 pair |
| Date: | 2022-10-24 15:01:54 |
| Message-ID: | Y1ao4uH2OG8d5N96@frastr-dev |
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| Thread: | |
| Lists: | pgsql-sql |
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
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