PostgrSQL UNION by key

Question

Can't come up with easy solution how to union tables with same columns but from second table add only rows which are present in first table.

t1:

id	A	B	C
1	xx	r	g
2	cc	r	g
5	d	g	e

t2:

id	A	B	C
101	jyj	u	j
5	y	jku	u
12	y	r	j

desired t1 union t2:

id	A	B	C
1	xx	r	g
2	cc	r	g
5	d	g	e
5	y	jku	u

Appreciate any help.

Answer 1

We can use an IN clause and say the id of table 2 must appear in table 1:

SELECT id, A, B, C
FROM t1
UNION ALL
SELECT id, A, B, C
FROM t2
WHERE t2.id IN (SELECT id FROM t1);

Try out: db<>fiddle