Re: Selecting exactly one row for each column value

Am Dienstag, 6. März 2007 16:03 schrieb Florian Weimer:

> a | b | c
> ---+---+---
> 5 | 6 | 7
> 2 | 3 | 4
> 1 | 2 | 3

Hi,
couldn't you accomplish this by:

select distinct on (a) * from tablename order by a;

here:

create table tab (a int,b int,c int);
insert into tab values (1,2,3);
insert into tab values (5,6,7);
insert into tab values (1,2,3);
insert into tab values (2,3,4);
insert into tab values (1,2,2);
insert into tab values (2,3,4);

select * from tab;
a | b | c
---+---+---
1 | 2 | 3
5 | 6 | 7
1 | 2 | 3
2 | 3 | 4
1 | 2 | 2
2 | 3 | 4
(6 rows)

select distinct on (a) * from tab order by a;
a | b | c
---+---+---
1 | 2 | 3
2 | 3 | 4
5 | 6 | 7
(3 rows)

my regards,

Stefan

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