Question

Tables bugs and dependencies looks like this:

select * from bugs; 
+--------+--------+
| bug_id | status |
+--------+--------+
|     20 | NEW    |
|     45 | CLOSED |
|     47 | NEW    |
|     30 | NEW    |
|     50 | CLOSED |
+--------+--------+


select * from dependencies;
+-----------+---------+
| dependson | blocked |
+-----------+---------+
|        20 |      45 |
|        20 |      47 |
|        30 |      50 |
+-----------+---------+

Expected result of join query: 30

What? Extract only 30 from column dependson, table dependencies because 30 is the only ( NEW status ) one which blocks ( col: blocked-50 ) a bug whose status is CLOSED.
Although the dependson entry 20 is blocking 45 which is CLOSED but it also blocks 47 which is not CLOSED.

Note: Both the columns dependson and blocked are foreign key of bug_id.

I tried different queries but not able to get proper one still… Can anybody please help ?

Update: need status only NEW not all.

Answer 1

Try this query –

SELECT b.* FROM bugs b
  JOIN (
    SELECT
      d.*
    FROM dependencies d
      JOIN bugs b
        ON b.bug_id = d.blocked
    GROUP BY d.dependson
      HAVING COUNT(IF(status = 'CLOSED', status, NULL)) = COUNT(*)
  ) t
  ON b.bug_id = t.dependson