Oracle 21c

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CREATE TABLE table1 (col1, col2, col3, col4, col20) AS
SELECT LEVEL, LEVEL, LEVEL, LEVEL, LEVEL FROM DUAL CONNECT BY LEVEL <= 10000 UNION ALL
SELECT LEVEL, LEVEL, LEVEL, LEVEL, LEVEL FROM DUAL CONNECT BY LEVEL <= 9;
10009 rows affected

EXPLAIN PLAN FOR
DELETE FROM table1 t
WHERE EXISTS(
  SELECT 1
  FROM   (
    SELECT ROW_NUMBER() OVER (
             PARTITION BY col1, col2, col3, col4, col20
             ORDER BY rowid
           ) AS rn
    FROM   table1
  ) x
  WHERE x.ROWID = t.ROWID
  AND   x.rn > 1
);
SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY());

PLAN_TABLE_OUTPUT

Plan hash value: 1468155324

--------------------------------------------------------------------------------

| Id  | Operation             | Name   | Rows  | Bytes | Cost (%CPU)| Time     |

--------------------------------------------------------------------------------

|   0 | DELETE STATEMENT      |        | 10009 |   361K|    25   (4)| 00:00:01 |

|   1 |  DELETE               | TABLE1 |       |       |            |          |

|*  2 |   HASH JOIN           |        | 10009 |   361K|    25   (4)| 00:00:01 |

|   3 |    TABLE ACCESS FULL  | TABLE1 | 10009 |   117K|    12   (0)| 00:00:01 |

|*  4 |    VIEW               |        | 10009 |   244K|    13   (8)| 00:00:01 |

|   5 |     WINDOW SORT       |        | 10009 |   195K|    13   (8)| 00:00:01 |

|   6 |      TABLE ACCESS FULL| TABLE1 | 10009 |   195K|    12   (0)| 00:00:01 |

--------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

   2 - access("X".ROWID="T".ROWID)

   4 - filter("X"."RN">1)

EXPLAIN PLAN FOR
DELETE FROM table1 t
WHERE ROWID IN (
  SELECT ROWID
  FROM   (
    SELECT ROW_NUMBER() OVER (
             PARTITION BY col1, col2, col3, col4, col20
             ORDER BY rowid
           ) AS rn
    FROM   table1
  )
  WHERE rn > 1
);
SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY());

PLAN_TABLE_OUTPUT

Plan hash value: 1468155324

--------------------------------------------------------------------------------

| Id  | Operation             | Name   | Rows  | Bytes | Cost (%CPU)| Time     |

--------------------------------------------------------------------------------

|   0 | DELETE STATEMENT      |        | 10009 |   361K|    25   (4)| 00:00:01 |

|   1 |  DELETE               | TABLE1 |       |       |            |          |

|*  2 |   HASH JOIN           |        | 10009 |   361K|    25   (4)| 00:00:01 |

|   3 |    TABLE ACCESS FULL  | TABLE1 | 10009 |   117K|    12   (0)| 00:00:01 |

|*  4 |    VIEW               |        | 10009 |   244K|    13   (8)| 00:00:01 |

|   5 |     WINDOW SORT       |        | 10009 |   195K|    13   (8)| 00:00:01 |

|   6 |      TABLE ACCESS FULL| TABLE1 | 10009 |   195K|    12   (0)| 00:00:01 |

--------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

   2 - access(ROWID=ROWID)

   4 - filter("RN">1)