Oracle 21c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
ALTER SESSION SET NLS_TIMESTAMP_FORMAT = 'YYYY-MM-DD HH24:MI:SS.FF';
CREATE TYPE string_varray IS VARRAY(10) OF VARCHAR2(30);
CREATE TABLE table_name (Customer_Reference, Order_no, Position, Item, Quantity) AS
SELECT 'AAA123', '001', 1, 'Apples',  12 FROM DUAL UNION ALL
SELECT 'AAA123', '001', 2, 'Oranges',  3 FROM DUAL UNION ALL
SELECT 'AAA123', '001', 3, 'Pears',    9 FROM DUAL UNION ALL
SELECT 'AAA123', '001', 4, 'Grapes',  18 FROM DUAL UNION ALL
SELECT 'AAA123', '002', 1, 'Apples',  12 FROM DUAL UNION ALL
SELECT 'AAA123', '002', 2, 'Oranges',  3 FROM DUAL UNION ALL
SELECT 'AAA123', '002', 3, 'Pears',    9 FROM DUAL UNION ALL
SELECT 'AAA123', '002', 4, 'Grapes',  18 FROM DUAL UNION ALL
SELECT 'AAA123', '003', 1, 'Apples',  12 FROM DUAL UNION ALL
SELECT 'AAA123', '003', 2, 'Oranges',  3 FROM DUAL UNION ALL
SELECT 'AAA123', '003', 3, 'Pears',    9 FROM DUAL UNION ALL
SELECT 'AAA123', '003', 5, 'Grapes',  18 FROM DUAL UNION ALL
SELECT 'AAA123', '004', 1, 'Apples',  12 FROM DUAL UNION ALL
SELECT 'AAA123', '004', 2, 'Oranges',  3 FROM DUAL UNION ALL
SELECT 'AAA123', '004', 3, 'Pears',   10 FROM DUAL UNION ALL
SELECT 'AAA123', '004', 4, 'Grapes',  18 FROM DUAL;
16 rows affected

WITH orders (customer_reference, order_no, num_positions) AS (
  SELECT customer_reference,
         order_no,
         COUNT(position)
  FROM   table_name
  GROUP BY
         customer_reference,
         order_no
)
SELECT o1.customer_reference,
       o1.order_no,
       o2.order_no
FROM   orders o1
       INNER JOIN orders o2
       ON (   o1.customer_reference = o2.customer_reference
          AND o1.order_no           < o2.order_no
          AND o1.num_positions      = o2.num_positions)
WHERE NOT EXISTS (
  (
    SELECT position, item, quantity
    FROM   table_name t1
    WHERE  t1.customer_reference = o1.customer_reference
    AND    t1.order_no           = o1.order_no
  MINUS
    SELECT position, item, quantity
    FROM   table_name t2
    WHERE  t2.customer_reference = o2.customer_reference
    AND    t2.order_no           = o2.order_no
  )
  UNION ALL
  (
    SELECT position, item, quantity
    FROM   table_name t2
    WHERE  t2.customer_reference = o2.customer_reference
    AND    t2.order_no           = o2.order_no
  MINUS
    SELECT position, item, quantity
    FROM   table_name t1
    WHERE  t1.customer_reference = o1.customer_reference
    AND    t1.order_no           = o1.order_no
  )
)


CUSTOMER_REFERENCE
ORDER_NO
ORDER_NO


AAA123
001
002