query to count number of unique relations - sql

Question

I have 3 tables:
t_user (id, name)
t_user_deal (id, user_id, deal_id)
t_deal (id, title)
multiple user can be linked to the same deal. (I'm using oracle but it should be similar, I can adapt it)
How can I get all the users (name) with the number of unique user he made a deal with.
let's explain with some data:
t_user:
id, name
1, joe
2, mike
3, John
t_deal:
id, title
1, deal number 1
2, deal number 2
t_user_deal:
id, user_id, deal_id
1, 1, 1
2, 2, 1
3, 1, 2
4, 3, 2
the result I expect:
user_name, number of unique user he made a deal with
Joe, 2
Mike, 1
John, 1
I've try this but I didn't get the expected result:
SELECT tu.name,
count(tu.id) AS nbRelations
FROM t_user tu
INNER JOIN t_user_deal tud ON tu.id = tud.user_id
INNER JOIN t_deal td ON tud.deal_id = td.id
WHERE
(
td.id IN
(
SELECT DISTINCT td.id
FROM t_user_deal tud2
INNER JOIN t_deal td2 ON tud2.deal_id = td2.id
WHERE tud.id <> tud2.user_id
)
)
GROUP BY tu.id
ORDER BY nbRelations DESC
thanks for your help

Answer 1

This should get you the result
SELECT id1, count(id2),name
FROM (
SELECT distinct tud1.user_id id1 , tud2.user_id id2
FROM t_user_deal tud1, t_user_deal tud2
WHERE tud1.deal_id = tud2.deal_id
and tud1.user_id <> tud2.user_id) as tab, t_user tu
WHERE tu.id = id1
GROUP BY id1,name

Answer 2

Something like
select name, NVL (i.ud, 0) ud from t_user join (
SELECT user_id, count(*) ud from t_user_deal group by user_id) i on on t_user.id = i.user_id
where i.ud > 0
Unless I'm missing somethig here. It actually sounds like your question references having a second user in the t_user_deal table. The model you've described here doesn't include that.

Answer 3

PostgreSQL example:
create table t_user (id int, name varchar(255)) ;
create table t_deal (id int, title varchar(255)) ;
create table t_user_deal (id int, user_id int, deal_id int) ;
insert into t_user values (1, 'joe'), (2, 'mike'), (3, 'john') ;
insert into t_deal values (1, 'deal 1'), (2, 'deal 2') ;
insert into t_user_deal values (1, 1, 1), (2, 2, 1), (3, 1, 2), (4, 3, 2) ;
And the query.....
SELECT
name, COUNT(DISTINCT deal_id)
FROM
t_user INNER JOIN t_user_deal ON (t_user.id = t_user_deal.user_id)
GROUP BY
user_id, name ;
The DISTINCT might not be necessary (in the COUNT(), that is). Depends on how clean your data is (e.g., no duplicate rows!)
Here's the result in PostgreSQL:
name | count
------+-------
joe | 2
mike | 1
john | 1
(3 rows)