Re: 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

select id1, id2 from table where id1<id2;

Mit freundlichen Grüßen

Martin Stöcker
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Von: Shaozhong SHI <shishaozhong(at)gmail(dot)com>
Gesendet: Montag, 24. Oktober 2022 16:44
An: pgsql-sql <pgsql-sql(at)lists(dot)postgresql(dot)org>
Betreff: 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

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(at)gmail(dot)com>
Sent: Monday, October 24, 2022 4:44 PM
To: pgsql-sql <pgsql-sql(at)lists(dot)postgresql(dot)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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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(at)gmail(dot)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

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

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

On Mon, Oct 24, 2022 at 8:02 AM William Alves Da Silva <
william_silva(at)unochapeco(dot)edu(dot)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