Hello,
> I have a complex query question whose answer I think would help me
to
> understand subselects and aggregates better. I have a table with four
> columns of interest:
>
> id (int primary key), loc_title (varchar null), loc_value (float
> null), loc_unit (varchar null)
>
> I want the output columns to be:
> (1) each distinct value of loc_title, sorted
> (2) an id of a record containing that loc_title
> (3) the loc_value for the record in column 2
> (4) the loc_unit for the record in column 2
>
> I don't care as much how the records for columns 2-4 are chosen. It
> could be max(loc_value), min(id), or something else. I just need some
> sample records to test my program against.
>
> Is this something I should be able to do with a single query with
a
> subselect, or is it too much for one query? I tried a few ways and
> none of them were syntactically valid.
Will this do?
test=# select * from myt;
id | loc_title | loc_value | loc_unit
----+-----------+-----------+----------
1 | AA |
80 | 10
2 | AA |
80 | 10
3 | BB |
80 | 10
4 | AA |
80 | 10
5 | BB |
80 | 10
(5 rows)
test=# select a.* from myt a where id in (select min(id)
from myt group by loc_title) order by loc_title;
id | loc_title | loc_value | loc_unit
----+-----------+-----------+----------
1 | AA |
80 | 10
3 | BB |
80 | 10
(2 rows)
Regards,
Jayadevan
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