Question

我的桌子有两列，名称和访问过的国家：

Name   Subjects
mike   england
maria  china
james  russia
mike   mexico
maria  france
laurel england
...    ...

现在我想写一个查询，显示访问过两个国家的人数，三，四等，最多十个。

最终结果如下：

Number of countries -> number of people
10                  -> 5
9                   -> 13
8                   -> 24
and so on.

那么我该如何处理呢？有什么建议吗？

Answer 1

为您的表考虑以下架构（我将其命名为subject，并且为了唯一键而添加了id列）

CREATE TABLE `subjects` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
`country` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=latin1

以下查询可以达到您想要的结果

SELECT a.c AS num_of_countries, COUNT(*) AS num_of_people 
FROM 
    (SELECT `country`, COUNT(*) AS c FROM subjects GROUP BY 1) a 
GROUP BY 1

Answer 2

试试这个：

SELECT t2.number_of_country, 
       count(t1.Name) number_of_people
FROM tableName t1
INNER JOIN 
    (SELECT Name, count(Subjects) number_of_country
     FROM tableName 
     GROUP BY Name) t2 ON t2.Name = t1.Name
GROUP BY t2.number_of_country

数据透视表的SQL查询

2 个答案: