Re: Combining two queries

>I have a table called friends with a user_id and a friend_id (both of these relate to an id in a users table).
>For each friend relationship there are two rows. There are currently ONLY reciprocal relationships. So if user ids 1 and 2 are friends there will be two rows (1,2) and (2,1).
>For 2 arbitrary ids, I need a query to get two pieced of data:
> * Are the two users friends?
> * How many friends do the two users have in common.
>Is there a way to do this with one query? Currently I've only been able to figure out how to do it with two.
>SELECT
> EXISTS(
> SELECT 1
> FROM friends
> WHERE user_id = 166324 AND friend_id = 166325) AS friends,
> (SELECT COUNT(1)
> FROM friends f1 JOIN friends f2 ON f1.friend_id = f2.friend_id
> WHERE f1.user_id = 166324 AND f2.user_id = 166325) AS mutual;
>I'm wondering if there is a better way to do this using only one query. I've tried a couple of GROUP BY approaches but they haven't worked.
>

Hi,
this should do the job, but requires an additional check constraint user_id <> friend_id to be on the safe side:

SELECT count(case when c1=1 then true end)=1 as are_friend,
count(*)-1 as common_friends
FROM
(
SELECT count(*) as c1
FROM friends
WHERE user_id IN (USER1, USER2)
GROUP BY case when user_id = USER2 then USER1 else USER1 end,
friend_id
HAVING COUNT (*) =2
OR COUNT(case when friend_id =USER1 then true end)=1
) q1

regards,
Marc Mamin