[lvan]

You need Delayed (the default type of join) between t1 and t2
Additionally you will need to adjust the t1 query (e.g. in the t1 datasource init method, look for examples in standard forms) in the code and add "Exist t2" condition that you need.

p.s. consider changing the design, it looks kinda wrong - this type of joins should never came up in normal developments.