CREATE OR REPLACE FUNCTION validate_leave(p_empid NUMBER)
RETURN VARCHAR2
AS
BEGIN
   RETURN TO_CHAR(p_empid);
END;

CREATE TABLE test (EMP_ID NUMBER, FIRST_NAME VARCHAR2(255), LAST_NAME VARCHAR2(255) NOT NULL)

INSERT INTO test VALUES (1, 'Gerald', 'Venzl')

INSERT INTO TEST VALUES (2, 'Tom', 'Drake')

COMMIT

SELECT regexp_substr(Validate_Leave(emp_id),'[a-zA-Z0-9]+',1,level) leave_name
FROM test
CONNECT BY level < regexp_count(Validate_Leave(emp_id),',') + 2

DECLARE
   TYPE t_emp_id IS TABLE OF VARCHAR2(255);
   coll_emp_id   t_emp_id;
BEGIN
   SELECT regexp_substr(Validate_Leave(emp_id),'[a-zA-Z0-9]+',1,level) leave_name
      BULK COLLECT INTO coll_emp_id
      FROM test
         CONNECT BY level < regexp_count(Validate_Leave(emp_id),',') + 2;
END;