带有子句的sql问题

Question

我正在尝试使用最常用的 ram 配置查找每个模型的查询。

表：

PC (code, model, speed, ram, hd, cd, price)

到目前为止，我能够列出每个型号的每个 ram 配置以及 ram 配置的使用次数。

select model, ram, max(config)
  from (select model,ram,count(ram) as config
          from pc 
         group by model, ram)
 group by model, ram

输出：

MODEL   RAM  MAX(CONFIG)
------- ---- -----------
1232    64   2
1232    32   2
1233    128  3
1121    128  3
1233    64   1
1260    32   1

当我尝试列出具有最常用内存的模型时遇到问题。

select model, ram
  from (select model, ram, count(ram) as config
          from pc 
         group by model, ram)
 group by model
having config = max(config);


Error : ORA-00979: not a GROUP BY expression

Answer 1

with x as 
(select model,ram,count(ram) as config
from pc 
group by model,ram)
, y as 
(select model, max(config) as mxconfig from x group by model)
select x.model, x.ram --choose max(x.ram) or min(x.ram) in case of a tie and group by x.model
from x join y on x.model = y.model and x.config = y.mxconfig

此解决方案使用cte 来实现您所需要的。如果您需要在配置平局时获得max 或min ram，则您应该在模型上再添加一个group by。

Answer 2

我认为您正在寻找的是：

SELECT model,ram FROM (SELECT model,ram,count(ram) AS config
FROM pc 
GROUP BY model,ram)
WHERE config=max(config)

记录应该已经按您的子查询分组

Answer 3

一种方法是使用窗口函数：

select model, ram
from (select model, ram,
             row_number() over (partition by model order by count(*) desc) as seqnum
      from pc 
      group by model, ram
     ) mr
where seqnum = 1;