sql - 通过查询获取组中每条记录的MAX值

Question

我有一个 SQL 查询，如下所示:

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

结果如下:

 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

我怎样才能获得每个客户的最大数量，以便得到类似的结果

 0 1 19086
 1 1 472
 2 1 292

提前致谢!

Answer 1

通过 row_number() 使用子查询:

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 ;

请注意，如果出现平局，这将任意返回其中一行。如果您想要所有这些，请使用 rank() 或 dense_rank()。