为具有约束的列选择最大值

Question

表格如下

公司，垂直，计数

对于每家公司，我想获得基于具有最高计数的特定垂直的计数总和

公司垂直计数 IBM 财务 10 IBM 研发 5 IBM 公关 2

我想得到以下输出

IBM 财务 17

Answer 1

这是"How to get the MAX row"问题的一个转折点（DBA.SE链接）

1. 通过简单的聚合获得每个公司的总垂直度和最高垂直度
2. 使用这些来识别源表中的行

类似的东西，未经测试

SELECT
    t.Company, t.Vertical, m.CompanyCount
FROM
    ( --get total and highest vertical  per Company
    SELECT
        COUNT(*) AS CompanyCount,
        MAX(Vertical) AS CompanyMaxVertical,
        Company
    FROM MyTable
    GROUP BY Company
    ) m
    JOIN --back to get the row for that company with  highest vertical
    MyTable t ON m.Company = t.Company AND m.CompanyMaxVertical = t.Vertical

编辑：这比 ROW_NUMBER 更接近标准 SQL，因为我们不知道平台

Answer 2

SELECT company,
       vertical,
       total_sum
FROM (
    SELECT Company, 
           Vertical, 
           sum(counts) over (partition by null) as total_sum,
           rank() over (order by counts desc) as count_rank
    FROM the_table
) t
WHERE count_rank = 1

Answer 3

select Company,
       Vertical,
       SumCounts
from (       
        select Company,
               Vertical,
               row_number() over(partition by Company order by Counts desc) as rn,
               sum(Counts) over(partition by Company) as SumCounts
        from YourTable
     ) as T
where rn = 1

Answer 4

自联接应该这样做。

select company, vertical, total_count
from(
    select sum(counts) as total_count
    from table
    )a
cross join table
where counts=(select max(counts) from table);

根据您的 RDBMS，您还可以使用窗口函数（例如 sum(count) over () as total_count），而不必担心交叉连接。