Re: Limiting to sub-id in a query ?

On Wed, Oct 26, 2016 at 9:22 AM, Tim Smith <randomdev4+postgres(at)gmail(dot)com>
wrote:

> Hi,
>
> I've been trying various GROUP BY but these all end up erroring out,
> so maybe I'm using the wrong tool for the job (or, more likely, the
> required query is beyond my level of SQL-fu !).
>
> CREATE TABLE IF NOT EXISTS names (
> main_id bigint,
> sub_id bigint,
> name text
> );
>
> create unique index IF NOT EXISTS name_idx on names(main_id,sub_id);
> insert into names(main_id,sub_id,name) values(1,2,'Bob');
> insert into names(main_id,sub_id,name) values(1,1,'Baby Bob');
> insert into names(main_id,sub_id,name) values(100,200,'Tom');
> insert into names(main_id,sub_id,name) values(100,100,'Jerry');
>
>
> The desired output is one row per main_id, with the desired row being
> the one with the lowest sub_id, i.e.
>
> select.......
>
> main_id | sub_id | name
> ---------+------------+-------------------
> 1 | 1 | Baby Bob
> 100 | 100 | Jerry
>
>
​Try (not tested):​

​SELECT DISTINCT ON (main_id) main_id, sub_id, name
FROM names
ORDER BY main_id, sub_id ASC;
​
David J.