Stewart Arthur Campbell (11/4/2013)
Agree with Paul
without table definitions, it was difficult to make an informed decision.
Without table definitions it's impossible to make an informed decision!
From my testing, it seems that if there is an index on "city" in the "contacts" table, then the execution plan will feature a merge join (if there is only an index on "city" in the "contacts2" table it will not).
So, from the information given in the question, all you can say is that the answer is either "merge join" OR "none of the above".