WITH FULLNAME_LIST AS(
    SELECT
        EMP_CODE
        ,REPLACE(EMP_LAST_NAME,' ','') || REPLACE(EMP_FIRST_NAME,' ','') AS FULLNAME
    FROM EMP
    WHERE VALID_FLG = 1
)

SELECT 
    EMP_CODE AS CODE
    ,EMP_LAST_NAME AS SURNAME
    ,EMP_FIRST_NAME AS NAME
FROM EMP NATURAL JOIN FULLNAME_LIST AS e
WHERE VALID_FLG = 1 AND EXISTS (SELECT 1 FROM FULLNAME_LIST WHERE e.FULLNAME = FULLNAME GROUP BY FULLNAME HAVING COUNT(FULLNAME) > 1) 
ORDER BY
    FULLNAME, CODE