TSQL按顺序最大化多列

Question

我的示例源代码如下

declare @t1 as table
(
    site varchar(max),
    service varchar(max),
    yr integer, 
    mo integer
)

insert into @t1
    select *
    from 
        (values
            ('site1', 'service1', 2021, 1),
            ('site1', 'service1', 2021, 10),
            ('site1', 'service1', 2020, 12),
            ('site1', 'service1', 2019, 9),
            ('site1', 'service2', 2014, 5),
            ('site1', 'service2', 2015, 6),
            ('site1', 'service2', 2016, 7),
            ('site1', 'service2', 2016, 9),
            ('site2', 'service3', 2010, 2),
            ('site2', 'service3', 2011, 1),
            ('site2', 'service3', 2012, 3),
            ('site2', 'service3', 2012, 8) ) t (a, b, c, d)

我想编写一个 SQL 查询，该查询将返回一个按站点和服务分组的表，它首先确定什么是 max yr，然后通过先前确定的 max yr 返回 mo 的最大值

我想要的输出如下

| site  | service  | maxYr | maxMo |
|-------|----------|-------|-------|
| site1 | service1 | 2021  | 10    |
| site1 | service2 | 2016  | 9     |
| site2 | service3 | 2012  | 8     |

我目前可以通过以下方式实现

select 
    a.site, a.service, a.yr as maxYr, max(a.mo) as maxMo
from 
    @t1 a
where 
    exists (select *
            from
                (select b.site, b.service, max(b.yr) as maxYr
                 from @t1 b
                 group by b.site, b.service) c
            where a.site = c.site
              and a.service = c.service
              and a.yr = c.maxYr)
group by 
    a.site, a.service, a.yr

我想知道是否有更好的方法可以通过单个查询来实现这一点，例如

select 
    site, service, max(yr) as maxYr, 
    max(mo) over (partition by site, service order by max(yr)) as maxMo 
from 
    @t1 
group by 
    site, service

如果我需要像Yr-Month-Date 这样进行进一步的聚合，我可能会更容易通过单个查询来实现。

Answer 1

如果你有答案，你也可以使用

ROW_NUMBER 按 SITE 和 SERVICE 降序排列的功能和顺序：

SELECT SITE,SERVICE,YR,MO 
FROM
(
    SELECT *, ROW_NUMBER() OVER(PARTITION BY SITE, SERVICE ORDER BY YR DESC, MO DESC ) RN
    FROM @t1
) X
WHERE X.RN = 1

Answer 2

您可以使用MAX() 和FIRST_VALUE() 窗口函数：

select distinct site, service,
       max(yr) over (partition by site, service) as maxYr,
       first_value(mo) over (partition by site, service order by yr desc, mo desc) as maxMo
from @t1;

请参阅demo。