I've never used SQL like services, but for sure you can have three subservices which does the SQL Queries and a wrapper service which calls the other three.
Hi Guru, any specific reason why you want to put 3 SQL statements in a single service? Sure it is possible but overloading a functionality should be used wisely.
As Carles said, you can create 3 SQL Queries and a wrapper service to call all three, but you would only be able to return the results of one. If you are intending to join the tables in memory, you can use infotable functions such as Intersect and Union to join the results together.