我有这样一个问题：

select
    yyyy_mm_dd,
    xml_id,
    feature,
    status
from
    schema.t1
where
    yyyy_mm_dd >= '2019-02-02'

union all

select
    yyyy_mm_dd,
    p_id as xml_id,
    'payment' as feature,
    case
        when payment = 1 then 1
        else 0
    end as status
from
    schema.t2
where
    yyyy_mm_dd >= '2019-02-02'

有没有办法让我保证 union 有比另一个更重要的约会吗？有了连接，我就可以用 on 条件 yyyy_mm_dd . 我想维持工会，但只到最大日期，这是在两个表中可用。
有没有比我提出的解决方案更有效的方法？

select
    c.yyyy_mm_dd,
    xml_id,
    feature,
    status
from
    schema.t1 c
left join(
    select
        max(yyyy_mm_dd) as yyyy_mm_dd
    from
        schema.t2
    where
        yyyy_mm_dd >= '2020-10-01'
) m on m.yyyy_mm_dd = c.yyyy_mm_dd
where
    c.yyyy_mm_dd >= '2020-10-01'
    and m.yyyy_mm_dd is null

union all

select
    c.yyyy_mm_dd,
    p_id as xml_id,
    'payment' as feature,
    case
        when payment = 1 then 1
        else 0
    end as status
from
    schema.t2 c
left join(
    select
        max(yyyy_mm_dd) as yyyy_mm_dd
    from
        schema.t1
    where
        yyyy_mm_dd >= '2020-10-01'
) m on m.yyyy_mm_dd = c.yyyy_mm_dd

where
    c.yyyy_mm_dd >= '2020-10-01'
    and m.yyyy_mm_dd is not null