How to compare 2 tables and display an id that is not in the second table?

Question

MySQL

Hello, there are 2 tables

test1
id
name
test2
id
test_id
type
name_test2

I need to find out which test.id is not in test2.test_id, if there are, add
2 lines for each not found id in the first line type = 1 in the second type=2. Something doesn't work, thanks for the help

Answer 1

insert into test2 (test_id, type)
select test.id, type_value from test1 
join (
select 1 as type_value
union all
select 2
) as types ON TRUE -- нужно декартово произведение
where not exists (select 1 from test2 where test2.test_id = test.id)

If mysql is ancient, then it might be more efficient to test left join test2 on test2.test_id = test.id where test2.test_id is null