mysql滑动订单问题

先根据以下代码来创建表MonthlyOrders并导入一定的数据

CREATE TABLE MonthlyOrders(
ordermonth DATE,
ordernum INT UNSIGNED,
PRIMARY KEY (ordermonth)
);

INSERT INTO MonthlyOrders SELECT '2010-02-01',23;
INSERT INTO MonthlyOrders SELECT '2010-03-01',26;
INSERT INTO MonthlyOrders SELECT '2010-04-01',24;
INSERT INTO MonthlyOrders SELECT '2010-05-01',27;
INSERT INTO MonthlyOrders SELECT '2010-06-01',26;
INSERT INTO MonthlyOrders SELECT '2010-07-01',32;
INSERT INTO MonthlyOrders SELECT '2010-08-01',34;
INSERT INTO MonthlyOrders SELECT '2010-09-01',30;
INSERT INTO MonthlyOrders SELECT '2010-10-01',31;
INSERT INTO MonthlyOrders SELECT '2010-11-01',32;
INSERT INTO MonthlyOrders SELECT '2010-12-01',33;
INSERT INTO MonthlyOrders SELECT '2011-01-01',31;
INSERT INTO MonthlyOrders SELECT '2011-02-01',34;
INSERT INTO MonthlyOrders SELECT '2011-03-01',34;
INSERT INTO MonthlyOrders SELECT '2011-04-01',38;
INSERT INTO MonthlyOrders SELECT '2011-05-01',39;
INSERT INTO MonthlyOrders SELECT '2011-06-01',35;
INSERT INTO MonthlyOrders SELECT '2011-07-01',49;
INSERT INTO MonthlyOrders SELECT '2011-08-01',56;
INSERT INTO MonthlyOrders SELECT '2011-09-01',55;
INSERT INTO MonthlyOrders SELECT '2011-10-01',74;
INSERT INTO MonthlyOrders SELECT '2011-11-01',75;
INSERT INTO MonthlyOrders SELECT '2011-12-01',14;

滑动订单问题是指为每个月返回上一年度（季度或月度）的滑动订单数，即每个月份N，返回N-11到月份N的订单总数。这里，假设月份序列中不存在间断。

执行下面的SQL查询实现每个月返回上一年度的滑动订单总数

SELECT
    DATE_FORMAT(a.ordermonth, '%Y%m') AS frommonth,
    DATE_FORMAT(b.ordermonth, '%Y%m') AS tomonth,
    SUM(c.ordernum) AS orders
FROM monthlyorders a
INNER JOIN monthlyorders b 
    ON DATE_ADD(a.ordermonth, INTERVAL 11 MONTH) = b.ordermonth
INNER JOIN monthlyorders c
    ON c.ordermonth BETWEEN a.ordermonth AND b.ordermonth
GROUP BY a.ordermonth,b.ordermonth;

运行结果如下图

该查询首先对MonthlyOrders表进行自连接。a表用做下边界(frommonth)，b表用做上边界(tomonth)。连接的条件为:

DATE_ADD(a.ordermonth, INTERVAL 11 MONTH) = b.ordermonth。

例如，a表中的2010年2月将匹配2011年1月。

完成自连接之后，需要对订单进行统计。这时需要再进行一次自连接，得到范围内每个月的订单数量。因此连接的条件为

c.ordermonth BETWEEN a.ordermonth AND b.ordermonth。

基于上述方法，我们还可以统计每个季度订单的情况，以此作为和同比增长的比较依据。

SELECT
    DATE_FORMAT(a.ordermonth, '%Y%m') AS frommonth,
    DATE_FORMAT(b.ordermonth, '%Y%m') AS tomonth,
    SUM(c.ordernum) AS orders
FROM monthlyorders a
INNER JOIN monthlyorders b 
    ON DATE_ADD(a.ordermonth, INTERVAL 2 MONTH) = b.ordermonth
    AND MONTH(a.ordermonth) % 3 = 1
INNER JOIN monthlyorders c
    ON c.ordermonth BETWEEN a.ordermonth AND b.ordermonth
GROUP BY a.ordermonth,b.ordermonth;

运行结果如下图