MYSQL select based on the selects - mysql

Question

You're help would be much appreciated...
If I have the following table and sample data... myGroupTable
group_Id : user_Id
1 : 3
1 : 7
1 : 100
2 : 3
2 : 7
2 : 100
2 : 104
4 : 42
4 : 98
4 : 13
I would like a sql statement that would...
Return a group_Id that has exactly the specified user_Id's in them.
eg... is there a group_Id that has User_Id's 3, 7 and 100
answer: group_id 1.
Please note that I dont want it to return a group_Id 2, as that also has a user_Id of 104 in it...
Kind regards J

Answer 1

SELECT
group_Id,
SUM(
IF user_Id = 3 THEN 1
ELSEIF user_Id = 7 THEN 2
ELSEIF user_Id = 100 THEN 4
ELSE 8
) AS bits
FROM myGroupTable
GROUP BY group_Id
HAVING bits=7
This assumes that you cannot have duplicate user_Ids for the same group_Id, eg this could never happens:
group user
1 3
1 3
Edit: You can build your query in the following way:
<?php
$ids = array(3, 7, 100);
$power = 2;
$query = "
SELECT
group_Id,
SUM(
IF user_Id = " .$ids[0]. " THEN 1 ";
foreach ($id in $ids) {
$query .= " ELSEIF user_Id = $id THEN " . $power;
$power = $power * 2;
}
$query .= " ELSE $power
) AS bits
FROM myGroupTable
GROUP BY group_Id
HAVING bits = " . ($power - 1);

Answer 2

Here's another alternative:
SELECT group_id, GROUP_CONCAT(user_id ORDER BY user_id) AS user_id_list
FROM group_user
GROUP BY group_id
HAVING user_id_list = '3,7,100'

Answer 3

another solution:
SELECT group FROM tbl WHERE group_id NOT IN (SELECT DISTINCT group_id FROM tbl WHERE user_id NOT IN(3,7,100)) AND user_id IN (3,7,100);

Answer 4

select group_id,
sum(
case user_id in(3,7,100)
when 1 then 1
else -99
end
) as must_be_3
from group_user
group by group_id
having must_be_3=3;