Are you sure that this is the query you run?
OK, but I still don't get it what you want to do as I can't figure out the question behind this.
The easiest thing is to set up a pice of test data (inlc. create table, inserts, SQL) and add it to the post. Which can others past to SQLA and can come up with an real solution - instead of guessing and seeing that description does not match.
Maybe you just forgot to use COALESCE(T1.id,T2.id), COALESCE(T1.date,T2.date), otherwise all non-existing rows from the left table will have NULLs and will be aggregated into a single row.