Question

I have the following tables within a database, that I am using to store the results of surveys:

Each time I speak to someone at a store (read Shop), I create a new transaction, with a date/time (tblTransaction.Created). Each transaction can have many question answers associated with it.

My problem is that 2 transactions could both contain different answers to the same question and I am trying to create an SQL query/procedure to return only the latest question answers for a given store.

Here’s an example:

I speak with someone at Some Shop Plc. and create a transaction on the 01/01/09 (transaction ID 1). In this transaction, I ask QuestionIDs 1 and 2. Then on the 10/01/09 I speak to them again, creating a new transaction (transaction ID 2) and answer questions 2 and 3.

I want to be able to show the list of latest answers; Question 1 from the first transaction and questions 2 and 3 from the second transaction.

Answer 1

SELECT      S.StoreID,      S.BranchName,      A.QuestionID,      T.Created,      A.* FROM      tblStore S INNER JOIN tblTransaction T ON      T.StoreID = S.StoreID INNER JOIN tblAnswer A ON      A.TransactionID = T.TransactionID AND      A.StoreID = S.StoreID WHERE NOT EXISTS           (           SELECT                T2.StoreID,                A2.QuestionID,                T2.TransactionID,                T2.CreatedDate           FROM                tblTransaction T2           INNER JOIN tblAnswer A2 ON                A2.TransactionID = T2.TransactionID AND                A2.StoreID = T2.StoreID           WHERE                T2.StoreID = T.StoreID AND                A2.QuestionID = A.QuestionID AND                T2.CreatedDate > T.CreatedDate           ) 

You can also do this by LEFT OUTER JOINing the subquery on the same criteria as in the WHERE clause and looking for a NULL value in it or you can remove the TransactionID from the subquery use a MAX() on the CreatedDate and look for a match that way with an INNER JOIN.

Keep in mind that this may not act how you are expecting if you have multiple transactions for the same store with the same created date. You may need to add an additional criteria there based on your business rules around that situation.