如何计算日期列的移动平均 DAYS

Question

我有这些列和数据示例数据：

CREATE TABLE Orders(customerid int, orderdate datetime, orderqty int);
INSERT into Orders(customerid, orderdate, orderqty) VALUES
    (1,'2020-11-25',100),(1,'2020-11-27',160),(2,'2020-12-05',3490),
    (1,'2020-11-29',293),(2,'2020-12-07',293),(1,'2020-12-01',382);

sqlfiddle： http://sqlfiddle.com/#!9/d90aaf/1/0

从这些数据中，我想找出每个客户在最后 3 行中的日期差异。 例如 output 将是：

customerid, last 3 orders average days between orders,sum of orderqty for last 3 order
1, 2,835
2, 2,3783

我已经尝试过 datediff() 但我无法通过 function 来实现这个结果。

Answer 1

无法为最近的 3 个订单找出更好的技巧。 这可行，但可能对大表性能不佳：

SELECT o3.customerid,DATEDIFF(Latest1,IFNULL(Latest3,Latest2))/IF(Latest3 IS NULL,1,2) AS avgDiff,SUM(oQ.orderqty) AS qty3orders FROM
(SELECT o2.*,MAX(ooo.orderdate) AS Latest3 FROM 
(SELECT o1.*,MAX(oo.orderdate) AS Latest2 FROM 
(SELECT customerid,MAX(orderdate) AS Latest1 FROM Orders GROUP BY customerid) o1 
JOIN Orders oo ON o1.customerid=oo.customerid AND oo.orderdate<o1.Latest1 GROUP BY o1.customerid) o2
LEFT JOIN Orders ooo ON o2.customerid=ooo.customerid AND ooo.orderdate<o2.Latest2 GROUP BY o2.customerid) o3
JOIN orders oQ ON o3.customerid=oQ.customerid AND oQ.orderdate>=COALESCE(o3.Latest3,o3.Latest2,o3.Latest1) GROUP BY o3.customerid