SQL - multiple rows in HAVING clause

Question

ok, So the query I would like to solve: I would like to express the following business rule: Display the groups (for a particular tutorial (tutorialID) and week (week)) that require additional reviews. So basically I need to determine the amount of members in a group, I then need to aggregate all the scrum reviews for that week and that group, and see if this amount equals the amount of members in the group. If it does, this means that all members have been reviewed for that week, and therefore does not need to be displayed. Assumptions: a member can only be reviews once per week. I've tried the following SQL, however I get the following error `Subquery returns more than 1 row` ``` SELECT groupName, g.groupId FROM `student` s, `group` g WHERE s.GroupId = g.GroupId AND s.GroupId IS NOT NULL AND s.tutorialId = 2 GROUP by s.GroupId AND s.GroupID = ( SELECT GroupId FROM student GROUP BY GroupId HAVING count(*)> ( SELECT count(*) FROM scrumreview r, student s WHERE r.reviewee = s.studentID…

Accepted Answer

Your inner query (starting on line 8) returns multiple `groupid`s. The equality operator `=` compares 1-to-1, but what you want is to compare 1-to-many, which you can do with `IN`.

So, to fix this, on line 7 change the code from this...

```
AND s.GroupID = (
```

...to this:

```
AND s.GroupID IN (
```

SQL - multiple rows in HAVING clause

Solution

Problem