CREATE TABLE ORDERS (
  ORDER_ID CHAR(8) NOT NULL PRIMARY KEY
);

INSERT INTO ORDERS (ORDER_ID) VALUES
  ('A'),
  ('B'),
  ('C');

CREATE TABLE SUBORDERS1 (
  ORDER_ID CHAR(8) NOT NULL REFERENCES ORDERS(ORDER_ID),
  SUBORDER_ID CHAR(8) NOT NULL,
  CONSTRAINT PK PRIMARY KEY (ORDER_ID, SUBORDER_ID)
);

CREATE TABLE SUBORDERS2 (
  ORDER_ID CHAR(8) NOT NULL REFERENCES ORDERS(ORDER_ID),
  SUBORDER_ID CHAR(8) NOT NULL,
  CONSTRAINT PK PRIMARY KEY (ORDER_ID, SUBORDER_ID)
);

INSERT INTO SUBORDERS1 (ORDER_ID, SUBORDER_ID) VALUES
  ('A', '1'),
  ('A', '2'),
  ('A', '3'),
  ('B', '1'),
  ('B', '2');

INSERT INTO SUBORDERS2 (ORDER_ID, SUBORDER_ID) VALUES
  ('A', '1'),
  ('A', '2'),
  ('A', '3'),
  ('B', '1'),
  ('C', '1'),
  ('C', '2');

WITH
Q1 AS (
  SELECT
    O.ORDER_ID,
    COUNT(*) AS COUNT
  FROM
    ORDERS O INNER JOIN SUBORDERS1 SO
      ON O.ORDER_ID = SO.ORDER_ID
  GROUP BY
    O.ORDER_ID
), 
Q2 AS (
  SELECT
    O.ORDER_ID,
    COUNT(*) AS COUNT
  FROM
    ORDERS O INNER JOIN SUBORDERS2 SO
      ON O.ORDER_ID = SO.ORDER_ID
  GROUP BY
    O.ORDER_ID
)
SELECT
  Q1.ORDER_ID
FROM
  Q1 INNER JOIN Q2
    ON Q1.ORDER_ID = Q2.ORDER_ID
    AND Q1.COUNT = Q2.COUNT;

SELECT
  Q1.ORDER_ID
FROM
  (
    SELECT
      O.ORDER_ID,
      COUNT(*) AS COUNT
    FROM
      ORDERS O INNER JOIN SUBORDERS1 SO
        ON O.ORDER_ID = SO.ORDER_ID
    GROUP BY
      O.ORDER_ID
  ) AS Q1
  INNER JOIN
  (
    SELECT
      O.ORDER_ID,
      COUNT(*) AS COUNT
    FROM
      ORDERS O INNER JOIN SUBORDERS2 SO
        ON O.ORDER_ID = SO.ORDER_ID
    GROUP BY
      O.ORDER_ID
  ) AS Q2
    ON Q1.ORDER_ID = Q2.ORDER_ID
    AND Q1.COUNT = Q2.COUNT;