计算SQL中不同的多个列的出现次数

Question

我正试图计算用户表中不同的一组城市和国家/地区的出现次数。

下表载列类似于：

userid city  country 
------ --------- -------------- 
1  Cambridge United Kingdom 
2  London  United Kingdom 
3  Cambridge United Kingdom 
4  New York United States 

我需要的是每个城市的名单，国家对与出现的次数：

Cambridge, United Kingdom, 2 
London, United Kingdom, 1 
New York, United States, 1 

目前我运行一个SQL查询得到不同的对：

$array = SELECT DISTINCT city, country FROM usertable 

然后将它读入PHP中的一个数组中，并循环遍历阵列，运行查询，以计算每个出现的每一行数组中：

SELECT count(*) FROM usertable 
WHERE city = $array['city'] 
AND country = $array['country'] 

我假设我的SQL的把握不足的是缺少的东西 - 这将是这样做的正确方法，最好不介入的PHP？

Answer 1

select city, country, count(*) 
from usertable 
group by city, country 

Answer 2

你需要的是一组由：

Select city, country, count(*) as counter 
from usertable 
group by city, country 

Answer 3

SELECT cityandcountry, count(*) as occurrences FROM (
    SELECT DISTINCT concat(city, country) FROM tablename 
) as baseview; 

如果你想城市和国家preformated

，或者

SELECT cityandcountry, count(*) as occurrences FROM (
    SELECT DISTINCT city, country FROM tablename 
) as baseview; 

如果不是。