Question

I have a table with application name and permissions given to the application. i need to find what are the applications that require both these

name   permissions
app1    perm1
app1    perm5
app1    perm6
app2    perm1
app2    perm8
app3    perm1
app3    perm6
app3    perm2
app3    perm4

How do i find the application names which has “perm1 and perm6” both….?

Answer 1

Here’s one way to do it.

SELECT t.name
  FROM mytable t
 GROUP BY t.name
HAVING MAX(IFNULL(t.permissions,'')='perm1')
     + MAX(IFNULL(t.permissions,'')='perm6') = 2
 ORDER BY t.name

We’re using a GROUP BY and aggregate functions, if we find a row for that has ‘perm1′, then t.permissons=’perm1’ returns a 1, otherwise it returns a 0. (We handle the case of a NULL by wrapping t.permissions in an IFNULL function.)

If we find both a ‘perm1’ and a ‘perm6’, then the HAVING predicate will evalulate to TRUE, and the row will be returned.

---

Another way to do it, using an EXISTS predicate to run a correlated subquery:

SELECT t.name
  FROM mytable t
 WHERE t.permissions = 'perm1'
   AND EXISTS 
       ( SELECT 1 
           FROM mytable s
          WHERE s.name = t.name
            AND s.permissions = 'perm6'
       )
 GROUP BY t.name
 ORDER BY t.name

---

or an equivalent, using an IN predicate:

 SELECT t.name
   FROM mytable t
  WHERE t.permissions = 'perm1'
    AND t.name IN 
        ( SELECT s.name
            FROM mytable s
           WHERE s.permissions = 'perm6'
             AND s.name IS NOT NULL
           GROUP BY s.name
        )
  GROUP BY t.name
  ORDER BY t.name

---

A fourth way to get it would be:

 SELECT t.name
   FROM mytable t
   JOIN mytable s
     ON t.name = s.name
    AND t.permissions = 'perm1'
    AND s.permissions = 'perm6'
  GROUP BY t.name
  ORDER BY t.name