Query on two PostgreSQL tables?

Question

PostgreSQL

Hello, help me to correctly form the request, something is confused.
There is a Field - an identifier in one table, there is another table in which the same identifiers (Users) may be present.
A query is needed that will display the user if he is in the first table, or in the second table + another condition for the second table, for example is_active.
The second table may contain several entries for this user.

Answer 1

SELECT `id` FROM `t1` UNION SELECT `id` FROM `t2` WHERE `is_active` = 1

Answer 2

SELECT id FROM (
  SELECT id FROM tbl1
  UNION
  SELECT id FROM tbl2 WHERE is_active = 1
) WHERE id = SOME_ID