delete from
    EMP
where EMP_CODE not in (
    select
        EMP_CODE
    from (
        select
            *
        from
            EMP e
        union all
        select
            *
        from
            EMP_INVALID ei
    )
    group by
        EMP_CODE
    having
        count(*) < 2 or
        sum(VALID_FLG) = 1
);