Question

I have a table like

id contact value
1  A       2
2  A       3
3  B       2
4  B       3
5  B       4
6  C       2

Now I would like to get the common maximum value for a given set of contacts.
For example:
if my contact set was {A,B} it would return 3;
for the set {A,C} it would return 2
for the set {B} it would return 4

What SQL statement(s) can do this?

Answer 1

Try this:

  SELECT value, count(distinct contact) as cnt
    FROM my_table
   WHERE contact IN ('A', 'C')
   GROUP BY value
   HAVING cnt = 2
   ORDER BY value DESC
   LIMIT 1

This is MySQL syntax, may differ for your database. The number (2) in HAVING clause is the number of elements in set.