通過查詢獲取組中每個記錄的MAX值

Question

我在SQL中的查詢看起來像這樣：

 select fldCustomer, fldTerminal, COUNT(fldbill)
 from tblDataBills
 group by fldCustomer, fldTerminal
 order by fldCustomer 

結果看起來像：

 fldCustomer    fldTerminal (number of bills)
 0  1   19086
 0  2   10
 0  5   236
 1  1   472
 1  5   3
 1  500 19
 2  1   292
 2  500 22

我如何獲得每個客戶的最大數量，所以我得到如下結果

 0 1 19086
 1 1 472
 2 1 292

提前致謝！

Answer 1

使用帶有row_number()的子查詢：

select fldCustomer, fldTerminal, cnt
from (select fldCustomer, fldTerminal, COUNT(*) as cnt,
             row_number() over (partition by fldCustomer order by count(*) desc) as seqnum
      from tblDataBills
      group by fldCustomer, fldTerminal
     ) db
where seqnum = 1
order by fldCustomer ;

請注意，在發生平局的情況下，這將任意返回行之一。 如果要全部使用，請使用rank()或dense_rank() 。

Answer 2

使用RANK()函數可能需要一些技巧

SELECT fldCustomer, fldTerminal, [(number of bills)]
FROM (
    SELECT fldCustomer, fldTerminal, COUNT(fldbill) [(number of bills)],
        RANK() OVER (PARTITION BY fldCustomer ORDER BY COUNT(fldbill) DESC) Ranking
    FROM tblDataBills
    GROUP BY fldCustomer, fldTerminal
) a
WHERE Ranking = 1