Question

Details:

Basically there are 2 MYSQL tables (contacts and transactions) and need to get contactid on the basis of two conditions

1. Get all the contacts (contactid) where there is no transaction at all
2. Get only those contacts who has one or more transactions but all of them are with Cancel status.

Help!?

Answer 1

You can actually accomplish this with a simple LEFT join… and look for NULL (not found). By doing a left-join, it gets all records from the left table regardless of a match on the right. So, if we set the join condition to your transactions table SPECIFICALLY for Cancelled = “No”, and we FIND a match, ignore that from the result set. If there are no records in transactions, OR all of them are set to Cancelled = “Yes”, they are excluded from the join condition and will thus be considered “none found”

select
      c.ContactID
   from
      Contacts c
         LEFT JOIN Transactions t
            on c.ContactID = t.ContactID
           AND t.Cancelled = "yes"
   where
      t.contactID is null