sql获取12个月份各个月份订单数并返回为一个数组格式，当月没有订单数的返回0，返回的数组是12个数，分别代表着12个月份的订单数

可以使用以下 SQL 语句来获取12个月份各个月份订单数并返回为一个数组格式：

SELECT COALESCE(SUM(CASE WHEN MONTH(order_date) = 1 THEN 1 ELSE 0 END), 0) AS month1,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 2 THEN 1 ELSE 0 END), 0) AS month2,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 3 THEN 1 ELSE 0 END), 0) AS month3,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 4 THEN 1 ELSE 0 END), 0) AS month4,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 5 THEN 1 ELSE 0 END), 0) AS month5,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 6 THEN 1 ELSE 0 END), 0) AS month6,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 7 THEN 1 ELSE 0 END), 0) AS month7,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 8 THEN 1 ELSE 0 END), 0) AS month8,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 9 THEN 1 ELSE 0 END), 0) AS month9,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 10 THEN 1 ELSE 0 END), 0) AS month10,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 11 THEN 1 ELSE 0 END), 0) AS month11,
       COALESCE(SUM(CASE WHEN MONTH(order_date) = 12 THEN 1 ELSE 0 END), 0) AS month12
FROM orders
WHERE order_date BETWEEN '2021-01-01' AND '2021-12-31'

这个 SQL 语句会在 `orders` 表中查找在 2021 年内的订单，并将它们按月份分组并计算每个月的订单数。如果当月没有订单，返回的值为 0。最后，这个 SQL 语句会返回一个包含 12 个数的数组，分别代表着 12 个月份的订单数。