表格构

+-------------------+---------------+------+-----+------------+----------------+
| Field             | Type          | Null | Key | Default    | Extra          |
+-------------------+---------------+------+-----+------------+----------------+
| order_id          | int(11)       | NO   | PRI | NULL       | auto_increment |
| order_date        | date          | NO   | MUL | 0000-00-00 |                |
| status            | tinyint(4)    | NO   | MUL | 0          |                |
| customer_id       | int           | NO   | MUL | 0          |                |
| first_name        | varchar(50)   | NO   |     | NULL       |                |
| last_name         | varchar(50)   | NO   |     | NULL       |                |
| email_address     | varchar(100)  | NO   |     | NULL       |                |
| country_code      | char(2)       | NO   | MUL | NULL       |                |
| order_total       | decimal(10,2) | NO   |     | 0.00       |                |
+-------------------+---------------+------+-----+------------+----------------+

如果你想得到一个国家的订单计数，你会运行一个这样的查询：如果你想得到一个由国家的订单计数，你会运行这样的查询：

SELECT country_code, COUNT(*)
FROM orders_header
GROUP BY country_code

从结果集的前几行可能看起来像这样：

+--------------+----------+
| country_code | count(*) |
+--------------+----------+
| AE           |       18 |
| AR           |       18 |
| AS           |       45 |
| AT           |       54 |
| AU           |     1277 |
| AZ           |        1 |
...

如果你想找出所有的国家只有一个订单，你可以把“group by ”和“having”这样的：

SELECT country_code, COUNT(*)
FROM orders_header
GROUP BY country_code
HAVING COUNT(*) = 1

这将只返回国家的代码，找出总数为1的，像这样：

+--------------+----------+
| country_code | COUNT(*) |
+--------------+----------+
| AZ           |        1 |
| BH           |        1 |
| GH           |        1 |
| KG           |        1 |
| KW           |        1 |
| MD           |        1 |
| NP           |        1 |
| QA           |        1 |
| WF           |        1 |
| ZW           |        1 |
+--------------+----------+
10 rows in set (0.18 sec)

作为另一个例子，如果你想找出所有的客户已经放置了超过5个订单，你可以使用相同的排序这样的查询：

SELECT customer_id, COUNT(*)
FROM orders_header
GROUP BY customer_id
HAVING COUNT(*) > 5

如果你想找到那些已经花费了超过1000美元的的订单

SELECT customer_id, SUM(order_total)
FROM orders_header 
GROUP BY email_address 
HAVING SUM(order_total) > 1000;