我有一个数据库，里面保存着客户的数据。我需要知道我们在各个城市和国家有多少客户。我必须用单个查询来完成它。
我的表是客户，我有城市和国家列(均为varchar)，其中包含有关它的信息。
所需的查询输出应如下所示:
City | NumberOfCustomers | Country | NumberOfCustomers |
--------------------------------------------------------
谢谢
最佳答案
select city, country, count(*) from tbl group by 1,2 with rollup
编辑以显示示例表和该查询的输出:
mysql> select * from location;
+-------+---------+
| city | country |
+-------+---------+
| City1 | US |
| City2 | US |
| City2 | US |
| City3 | CA |
| City3 | CA |
| City3 | JP |
+-------+---------+
6 rows in set (0.00 sec)
mysql> select city, country, count(*) from location group by 1,2 with rollup;
+-------+---------+----------+
| city | country | count(*) |
+-------+---------+----------+
| City1 | US | 1 |
| City1 | NULL | 1 |
| City2 | US | 2 |
| City2 | NULL | 2 |
| City3 | CA | 2 |
| City3 | JP | 1 |
| City3 | NULL | 3 |
| NULL | NULL | 6 |
+-------+---------+----------+
8 rows in set (0.01 sec)
关于MySQL 多列、单查询，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22235667/