Consider I have this table:
考虑我有这个表：
// Orders
OrderId Customer OrderDate
------------------------------
1 Jack 2018/05/01
2 Jack 2018/05/05
3 Jack 2018/05/15
4 Jack 2018/05/18
5 Jack 2018/05/21
6 Alex 2018/06/11
7 Alex 2018/06/12
8 Alex 2018/06/17
9 Alex 2018/06/18
// Ord
