Oracle 11g Release 2

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
select * from V$VERSION;


BANNER


Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

PL/SQL Release 11.2.0.2.0 - Production

CORE 11.2.0.2.0 Production

TNS for Linux: Version 11.2.0.2.0 - Production

NLSRTL Version 11.2.0.2.0 - Production


CREATE TABLE TEST_TAB_NAME (Customer_Reference, Order_, Position, Item, Quantity) as (
select 'AAA123', '001', 1, 'Apples',  12 from dual union all
select 'AAA123', '001', 2, 'Oranges', 03 from dual union all
select 'AAA123', '001', 3, 'Pears',   09 from dual union all
select 'AAA123', '001', 4, 'Grapes',  18 from dual union ALL
--same
select 'AAA123', '002', 1, 'Apples',  12 from dual union all
select 'AAA123', '002', 2, 'Oranges', 03 from dual union all
select 'AAA123', '002', 3, 'Pears',   09 from dual union all
select 'AAA123', '002', 4, 'Grapes',  18 from dual union all
--diff
select 'AAA123', '003', 1, 'Apples',  12 from dual union all
select 'AAA123', '003', 2, 'Peaches', 03 from dual union ALL
--diff
select 'AAA124', '004', 1, 'Pears',   09 from dual union all
select 'AAA124', '004', 2, 'Grapes',  18 from dual union all
select 'AAA124', '004', 3, 'Banana',  15 from dual union ALL --
--diff
select 'AAA124', '005', 1, 'Pears',   03 from dual union ALL --
select 'AAA124', '005', 2, 'Grapes',  09 from dual union all
select 'AAA124', '005', 3, 'Banana',  15 from dual
)
;
16 rows affected

WITH TAB_WITH_NB_ORDER_ITEMS AS (
SELECT t.*, COUNT(*)OVER(PARTITION BY CUSTOMER_REFERENCE, ORDER_) nb_oi
FROM TEST_TAB_NAME t
)
SELECT T1.CUSTOMER_REFERENCE,
     T1.ORDER_             AS ORDER_1,
     T2.ORDER_             AS ORDER_2
FROM TAB_WITH_NB_ORDER_ITEMS T1
JOIN TAB_WITH_NB_ORDER_ITEMS T2
  ON (
     T1.CUSTOMER_REFERENCE = T2.CUSTOMER_REFERENCE 
     AND T1.ORDER_    < T2.ORDER_
/*Is the comparison on "position" column relevant here ??? */  
     AND t1.POSITION  = t2.POSITION
     AND T1.ITEM      = T2.ITEM 
     AND T1.QUANTITY  = T2.QUANTITY 
     AND T1.NB_OI     = T2.NB_OI
     )
GROUP BY T1.CUSTOMER_REFERENCE, T1.ORDER_, T2.ORDER_
HAVING COUNT(*) = MAX(T1.NB_OI) /* anyway t1.nb_oi = t2.nb_oi*/
;


CUSTOMER_REFERENCE
ORDER_1
ORDER_2


AAA123
001
002