title: Rails batch select on multi column index
body: <p>I can't seem to get the query syntax down in Rails for doing a command like:</p>
  <p>SELECT * FROM table WHERE (colA = aaa AND colB = bbb) OR (colA = ccc AND colB = ddd) OR ...</p>
  <p>Where I would have 100+ of these queries hitting a composite index and each value of colA and colB is unique.</p>