How to find exact row match using IN in Where clause? - mysql

Question

I have two tables tbl_group AND tbl_members.
Here is snapshot of both the tables.
+----+------------+
| id | groupTitle |
+----+------------+
| 1 | Group 1 |
| 2 | Group 2 |
+----+------------+
+----+---------+--------+
| id | groupId | userId |
+----+---------+--------+
| 1 | 1 | 1 |
| 2 | 1 | 2 |
| 3 | 1 | 3 |
| 4 | 2 | 1 |
| 5 | 2 | 2 |
+----+---------+--------+
Now i want to create one more group with userId 3,2 but before that i want to check that is there any group which has same member 3 and 2 not any other.
i have used IN clause but it does not work.
SELECT DISTINCT groupId
FROM tbl_members
WHERE userId IN (3,2)
It is returning both the group though result would be empty.

Answer 1

We can try using INSERT INTO ... SELECT with an EXISTS clause which asserts that userId of 2/3 does not already occur for any group.
INSERT INTO tbl_members (groupId, userId)
SELECT groupId, userId
FROM (
SELECT 3 AS groupId, 2 AS userId UNION ALL SELECT 3, 3
) t
WHERE NOT EXISTS (SELECT 1 FROM tbl_members
WHERE userId IN (2, 3)
GROUP BY groupId
HAVING MIN(userId) <> MAX(userId));
You would also have to insert a new record into the tbl_group table for the new group.

Answer 2

SELECT DISTINCT groupId FROM tbl_members WHERE userId = '2'
INTERSECT
SELECT DISTINCT groupId FROM tbl_members WHERE userId = '3'

Answer 3

One way is to use conditional aggregation based filtering using GROUP BY with HAVING clause. We will use a query to get the groupId value which has userId values of 3 and 2 only. If the query does not return any such value; this implies that no such Group exists; hence you can create the group.
SELECT
groupId
FROM tbl_members
GROUP BY groupId
HAVING SUM(userId = 2) AND /* userID 2 exists */
SUM(userId = 3) AND /* userID 3 exists */
NOT SUM(userId NOT IN (2,3)) /* No other userId exists (other than 2,3) */

Answer 4

This returns groupId's where only 2 AND 3 are in the group.
Count of all userId's in the group - sum of 1 for records where userId = 2 or 3 has to be 0 if there are no other userid's in the group.
Sure this will work only if 2 and 3 don't repeat itself in the same group.
SELECT groupId
FROM tbl_members
GROUP BY groupId
HAVING COUNT(userId)-SUM(userId IN (2,3)) = 0

Answer 5

First inner query will decide all fetched groups have only two members that will reduce set of unnecessary records then second inner query take that group id and check whether there is no other member then 3,2 in that group, and finally whole query will give group id which has only 3,2 as member.
SELECT groupId
FROM tbl_members m
WHERE m.userId IN (3,2) AND
(SELECT COUNT(memberId) FROM tbl_members mmm WHERE mmm.groupId=m.groupId)=2 AND
(SELECT COUNT(memberId) FROM tbl_members mm WHERE mm.groupId=m.groupId AND
m.userId NOT IN (3,2))<=0
GROUP BY groupId

Answer 6

I think this query will give the group of values in userid (2,3), groupid (2,3)
from the table
SELECT count(1), userid ,groupid FROM tbl_members
WHERE groupid IN (3,2) and userid in (3,2)
group by userid, groupid;