Here is my sample dataset
这是我的样本数据集
id thing datetime price
----|-----|------------|----------
1 | A | 04/03/2009 | 399
2 | B | 04/03/2009 | 244
5 | C | 04/03/2009 | 555
3 | D | 04/03/2009 | 300
4 | A | 03/03/2009 | 200
6 | B | 03/03/2009 | 500
7 | C | 24/12/2008 | 600
8 | D | 01/01/2009 | 700
9 | A | 01/03/2009 | 250
10 | B | 01/03/2009 | 400
11 | C | 12/12/2008 | 300
12 | D | 20/01/2008 | 600
id th