I've created a SP (SP1) which returns a single row of data based on one input variable.
I'd now like to create another SP (SP2) which joins SP1. In other words, I have a table which lists the same variable used with SP1, and I'd like to join - like a loop against the possible variables listed in another table.
You can do something like that, for example, using OPENQUERY. But those are really hacks, and there is no straightforward way to join one stored procedure to another similar to what you might do with tables/views.
The best approach would be to write a new stored proc that joins the queries in the code within the stored proc.