danmcb wrote:
Hi
!'ve been wondering how to formulate a query to get a set of objects
out of a database, and am a bit stuck. I hope that someone here might
be able to help.
This is what the db looks like:
Table TYPES
id int primary key,
description text
Table GROUPS
id int primary key
description text
Tables WIDGETS
type_id int references TYPES(id),
group_id int references GROUPS(id),
primary key(type_id, group_id)
Now, given two type_id's, say A and B, I would like to find all groups
(or group_id's of course) that have a widget of both of these two
types.
There must be a more a elegant method but here's the first thing that
came to me:
SELECT group_id FROM widgets WHERE type_id = $1
AND group_id IN (
SELECT DISTINCT group_id FROM widgets WHERE type_id = $2
);
I trust you aren't planning to run this on billions of rows ...
b
---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
