ORACLE SQL CONVERTER FLAT SEPARADO POR VÍGULA EM COLUNAS

WITH flat AS (SELECT 'A,B,C,D' comma FROM DUAL)
SELECT  REGEXP_SUBSTR (comma, '[^,]+', 1, 1)    AS part_1
,       REGEXP_SUBSTR (comma, '[^,]+', 1, 2)    AS part_2
,       REGEXP_SUBSTR (comma, '[^,]+', 1, 3)    AS part_3
,       REGEXP_SUBSTR (comma, '[^,]+', 1, 4)    AS part_4
FROM    flat