3 ms·

also, no need to write test cases again if they can prove or disprove two queries.

• mulmen 9y ago
  You still need test cases to make sure the requirements have been satisfied. Even in the case where you know there is a problem with a query and show there is a difference with Cosette there is no guarantee that it will show the specific difference you are looking for. This is a fantastic tool but it doesn't replace testing.
  • akc2 9y ago
    fair enough. I was thinking more on the side of "this rewrite should be correct and indeed it is" by asking the tool to come up with a proof rather than doing extensive testing.
    • mulmen 9y ago
      Cosette can prove equivalency but not correctness. Unit testing can't prove correctness either but it can demonstrate that specific conditions are satisfied. If you have a query 1 that satisfies case a and b but then identify a bug and add case c you can write a query 2 which satisfies a, b and c and indeed Cosette may identify that case as the difference (or not!) but you still have no guarantee that you will not then discover case d which is not satisfied by 1 or 2 or a future 3.
    • deleted 9y ago
      [deleted]
    • ams6110 9y ago
      Even if the two queries are provably equivalent, that does not mean that the database engine will produce the same results for the two. There could be bugs in the implementation.