SQL多个组 - 可能吗？

Question

我有这个形式的查询：

SELECT e.date, SUM(e.size) as bytes 
FROM entries AS e 
GROUP BY e.date 
ORDER BY bytes DESC 

，我有一个名为客户端柱，它是由静态值（0,1,2,3），所以我希望得到这样的：

SELECT e.date, SUM(e.size) as bytes 
FROM entries AS e 
WHERE e.client = 0 
GROUP BY e.date 
ORDER BY bytes DESC 

重复为每个客户端类型，但在一个单一的查询来获取每一个客户端类型汇总尺寸的结果：

DATE | CLI0-SIZE | CLI1-SIZE | CLI2-SIZE | CLI3-SIZE 
2010-11-11  113   344   435   155 

Answer 1

你可以试试这个

SELECT e.date, 
    SUM(CASE WHEN e.client = 0 THEN e.size ELSE 0 END) as CLI0-SIZE, 
    SUM(CASE WHEN e.client = 1 THEN e.size ELSE 0 END) as CLI1-SIZE, 
    SUM(CASE WHEN e.client = 2 THEN e.size ELSE 0 END) as CLI2-SIZE, 
    SUM(CASE WHEN e.client = 3 THEN e.size ELSE 0 END) as CLI3-SIZE 
FROM entries AS e 
GROUP BY e.date 

Answer 2

关系数据库管理系统：Microsoft SQL Server的

这将返回以下布局：

date | client | bytes 
2010-11-11 | 2 | 435 
2010-11-11 | 1 | 344 
2010-11-11 | 3 | 155 
2010-11-11 | 0 | 113 

这将组的所有客户端类型，而不仅仅是0,1,2,3 - 我想你想要这个。

SELECT 
    e.date, 
    e.client, 
    SUM(e.size) AS bytes 
FROM 
    entries AS e 
GROUP BY 
    e.date, 
    e.client 
ORDER BY 
    bytes DESC 

然后，您可以在桌子上执行数据透视。