title: Check if two "select"s are equivalent
body: <p>Is there a way to check if two (non-trivial) select are equivalent?</p>
  
  <p>Initially I was hoping for a formally equivalence between two selects, but the answers in
  <a href="https://stackoverflow.com/questions/56895/proving-sql-query-equivalency">proving-sql-query-equivalency</a> stop me.</p>
  
  <p>For my actual need I can just check if the (actual) results of two selects are the same.</p>