DELETE FROM EMP
WHERE EXISTS (
    SELECT 1 FROM EMP_INVALID
    WHERE EMP_INVALID.EMP_CODE = EMP.EMP_CODE
    AND EMP_INVALID.VALID_FLG = '0'
    AND NOT EXISTS (
        SELECT 1 FROM EMP
        WHERE EMP.EMP_CODE = EMP_INVALID.EMP_CODE
        AND EMP.VALID_FLG = '1'
    )
);