SELECTING with multiple WHERE conditions on same column

Question

Ok, I think I might be overlooking something obvious/simple here... but I need to write a query that returns only records that match multiple criteria on the same column...<

Answer 1

Use:

  SELECT t.contactid
    FROM YOUR_TABLE t
   WHERE flag IN ('Volunteer', 'Uploaded')
GROUP BY t.contactid
  HAVING COUNT(DISTINCT t.flag) = 2

The key thing is that the counting of t.flag needs to equal the number of arguments in the IN clause.

The use of COUNT(DISTINCT t.flag) is in case there isn't a unique constraint on the combination of contactid and flag -- if there's no chance of duplicates you can omit the DISTINCT from the query:

  SELECT t.contactid
    FROM YOUR_TABLE t
   WHERE flag IN ('Volunteer', 'Uploaded')
GROUP BY t.contactid
  HAVING COUNT(t.flag) = 2