SQL Server 计数分组依据答案

【问题标题】：SQL Server Count on a grouped bySQL Server 计数分组依据
【发布时间】：2011-06-09 15:59:58
【问题描述】：

我有 3 张桌子。我想按 item.name 分组并计算可以在 idetail 中找到的次数。此查询只计算所有行而不是按行分组。

有人知道怎么解决吗？

SELECT i.name, COUNT(i.name)
FROM item AS i
INNER JOIN item_category AS ic ON i.i_category_id = ic.ic_id
INNER JOIN idetail AS id ON ic.ic_id = id.id_category_id
WHERE ic.ic_id = 1002
GROUP BY i.name

【问题讨论】：

一定有问题，或者我遗漏了一些东西。 This query only counts all rows not the grouped by rows. 先生，据我所知，此脚本通过分组计算 COUNT(*)，并且正确执行，即结果必须是每个 item.name 的数字，而不是所有行的计数。你实际上得到了什么输出？
我对你真正想要的东西也有点困惑——你能举个例子吗？也许您打算使用SELECT COUNT(DISTINCT i.name) . . . 或SELECT i.name, COUNT(id.id_id) FROM . . . LEFT JOIN idetail id . . . GROUP BY i.name 之类的东西？

标签： sql sql-server count group-by

【解决方案1】：

这就是你想要的：

select x.name
     , count(*) as cntNames
     , sum(x.cntDetails) as cntDetails
  from (
        SELECT i.name, COUNT(*) as cntDetails
          FROM item AS i
         INNER JOIN item_category AS ic ON i.i_category_id = ic.ic_id
         INNER JOIN idetail AS id ON ic.ic_id = id.id_category_id
         WHERE ic.ic_id = 1002
          -- NOTICE THE 2nd Value in the group by!
         GROUP BY i.name,id.id_category_id
       ) x
  group by name

【讨论】：

【解决方案2】：

Select  Count(*)
From    (
            Select i.name, Count(i.name)
            From item As I
                Join item_category As ic
                    On ic.ic_id = i.category_id
                Join idetail as ID
                    On ID.id_category_id = ic.ic_id
            Where ic.ic_id = 1002
            Group By i.name
            ) As Z

如果您想要所有三列并且您使用的是 SQL Server 2005+

With Items As
    (
    Select I.name, Count(i.name) As ItemCount
    From item As I
        Join item_category As ic
            On ic.ic_id = i.category_id
        Join idetail as ID
            On ID.id_category_id = ic.ic_id
    Where ic.ic_id = 1002
    Group By i.name
    )
Select Name, ItemCount
    ,   (
        Select Count(*)
        From Items
        ) As OverallCount
From Items

另一个更简单的版本，如果您使用的是 SQL Server 2005+。

Select i.name
    , Count(i.name) As CountByName
    , Count(*) Over() As TotalCount
From item As I
    Join item_category As ic
        On ic.ic_id = i.category_id
    Join idetail as ID
        On ID.id_category_id = ic.ic_id
Where ic.ic_id = 1002
Group By i.name

【讨论】：