Postgres 15

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CREATE TABLE t1 (id int, entity_type int);
INSERT INTO t1 VALUES
  (9, 3)
, (9, 4)
, (9, 5)
, (2, 3)
, (2, 5)
;

CREATE TABLE t2 (id int, entity_type int);
INSERT INTO t2 VALUES
  (1, 3)
, (1, 4)
;

CREATE TABLE

INSERT 0 5

CREATE TABLE

INSERT 0 2

SELECT id, array_agg(entity_type ORDER BY entity_type) AS arr
FROM   t1
GROUP  BY 1
HAVING array_agg(entity_type ORDER BY entity_type) @> (
   SELECT array_agg(entity_type ORDER BY entity_type)
   FROM   t2
   WHERE  id = 1
   );

id
arr

9
{3,4,5}

SELECT 1

SELECT t1.id
FROM   t2
JOIN   t1 USING (entity_type)
WHERE  t2.id = 1
GROUP  BY 1
HAVING count(*) = (SELECT count(*) FROM t2 WHERE id = 1);

id

9

SELECT 1