Обсуждение: How to find not unique rows in a table?

Assuming you have a table where some rows have the same values in all
columnes, how do you find these rows?

am  Wed, dem 08.10.2008, um 13:20:47 +0200 mailte A B folgendes:
> Assuming you have a table where some rows have the same values in all
> columnes, how do you find these rows?

You can use the ctid-column:

test=*# select * from dup;
 a | b
---+---
 1 | 1
 1 | 2
 2 | 1
 1 | 1
 3 | 3
 3 | 3
(6 rows)

test=*# select * from dup where (ctid,a,b) not in (select distinct on (a,b) ctid,* from dup);
 a | b
---+---
 1 | 1
 3 | 3
(2 rows)



Andreas
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Andreas Kretschmer
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On Wed, Oct 08, 2008 at 01:36:37PM +0200, A. Kretschmer wrote:
> test=*# select * from dup;
>  a | b
> ---+---
>  1 | 1
>  1 | 2
>  2 | 1
>  1 | 1
>  3 | 3
>  3 | 3
> (6 rows)
>
> test=*# select * from dup where (ctid,a,b) not in (select distinct on (a,b) ctid,* from dup);
>  a | b
> ---+---
>  1 | 1
>  3 | 3
> (2 rows)

another approach:
select a,b from dup group by a,b having count(*) > 1;

depesz

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A B wrote:
> Assuming you have a table where some rows have the same values in all
> columnes, how do you find these rows?

There is no reliable, time-independent way.
That's one reason why you have primary keys on tables.

There is the system column "ctid", but that may change any second.

Yours,
Laurenz Albe