T-SQL - How to write a conditional join

Question

I have a stored procedure with a number of parameters. I would like to write my query so that it joins with certain tables but only if a particular parameter has a value. Take

Answer 1

Yes, it's very simple. Do left joins on the address and groups. Then in the where clause...

(@group_id is null or g.group_id = @group_id)
and (@address_id is null or a.address_id = @address_id)