與contraint

Question

表列選擇最大值如下

 
Company, Vertical, Counts 

對於每個公司我想獲得具有最高計數

 
Company  Vertical    Counts 
IBM   Finance    10 
IBM   R&D     5 
IBM   PR     2 

我計數的基於特定垂直SUM想獲得以下輸出

 
IBM  Finance 17 

Answer 1

自聯接應該這樣做。

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); 

根據您的RDBMS，你也可以使用（超過（）作爲TOTAL_COUNT如SUM（計數）），而不必擔心交叉連接的窗口功能。

Answer 2

這是對的"How to get the MAX row"（DBA.SE鏈接）問題

1. 得到總的和最高的垂直每家公司在一個簡單的彙總
2. 使用這些標識源表中的行扭轉

事情是這樣的，未經檢驗

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 

埃德它：這是不是ROW_NUMBER更接近於標準的SQL，因爲我們不知道平臺

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

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