A simple way to debug if it's the table contents or something else that's causing the issue,is to add the following where-clause at the end of your SQL statement:
...and rownum = 1
If you still get two features,then it's probably not the database.On the other hand,if that fixes the problem then it's 99% certain that it's the table contents that actually contains several records that match your where-clause.
Can you share the exact contents of statement used in the SQLCreator?A screenshot would be perfect.
I suppose you have connected only the Result output port?
If you would have connected both Result and Initiator output ports,that would explain the duplicates.