Oracle 21c

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SELECT SYS.ODCIVARCHAR2LIST('a', 'b', 'c')(1) FROM DUAL;
ORA-03001: unimplemented feature

SELECT list(1)
FROM   (SELECT SYS.ODCIVARCHAR2LIST('a', 'b', 'c') AS list FROM DUAL);
ORA-00904: "LIST": invalid identifier

SELECT l.list(1)
FROM   (SELECT SYS.ODCIVARCHAR2LIST('a', 'b', 'c') AS list FROM DUAL) l;
ORA-00904: "L"."LIST": invalid identifier

SELECT (
         SELECT COLUMN_VALUE
         FROM   TABLE(s.shape.sdo_ordinates)
         FETCH FIRST ROW ONLY
       ) as startpoint_x
FROM  (
  select sdo_geometry('linestring(1 2, 3 4, 5 6)') as shape from dual
) s


STARTPOINT_X


1