mysql 统计各市1到12月份的订单量

您可以使用 MySQL 的 `SUM()` 函数来统计每个月的订单量。具体来说，您可以使用以下 SQL 语句：

SELECT city, SUM(CASE WHEN month = 1 THEN 1 ELSE 0 END) as 'Jan', 
SUM(CASE WHEN month = 2 THEN 1 ELSE 0 END) as 'Feb',
SUM(CASE WHEN month = 3 THEN 1 ELSE 0 END) as 'Mar',
SUM(CASE WHEN month = 4 THEN 1 ELSE 0 END) as 'Apr',
SUM(CASE WHEN month = 5 THEN 1 ELSE 0 END) as 'May',
SUM(CASE WHEN month = 6 THEN 1 ELSE 0 END) as 'Jun',
SUM(CASE WHEN month = 7 THEN 1 ELSE 0 END) as 'Jul',
SUM(CASE WHEN month = 8 THEN 1 ELSE 0 END) as 'Aug',
SUM(CASE WHEN month = 9 THEN 1 ELSE 0 END) as 'Sep',
SUM(CASE WHEN month = 10 THEN 1 ELSE 0 END) as 'Oct',
SUM(CASE WHEN month = 11 THEN 1 ELSE 0 END) as 'Nov',
SUM(CASE WHEN month = 12 THEN 1 ELSE 0 END) as 'Dec'
FROM orders
GROUP BY city;

在这个语句中，我们首先选择了城市和每个月的订单数量。然后，我们使用 `SUM()` 函数将所有订单按月份分组。最后，我们使用 `GROUP BY` 子句将每个城市的订单按月份分组。这样就可以得到每个城市每个月的订单量了。