数据如下所示:
num trddt clsprc
002107 2007-01-25 21.28
002107 2007-01-26 20.32
002107 2007-01-29 20.53
002107 2007-01-30 19.95
002107 2007-01-31 19.01
002107 2007-02-01 19.2
002107 2007-02-02 18.8
002107 2007-02-05 18.91
002107 2007-02-06 19.07
002107 2007-02-07 19.3
002107 2007-02-08 19.15
002107 2007-02-09 18.92
002107 2007-02-12 19.32
002107 2007-02-13 19.52
002107 2007-02-14 19.61
002107 2007-02-15 19.9
002107 2007-02-16 19.89
002107 2007-02-26 20.22
002107 2007-02-27 19.09
002108 2007-01-25 17.95
002108 2007-01-26 17.24
002108 2007-01-29 17.71
002108 2007-01-30 17.47
002108 2007-01-31 17.09
002108 2007-02-01 17.35
002108 2007-02-02 17.14
002108 2007-02-05 17.1
002108 2007-02-06 17.39
002108 2007-02-07 17.3
002108 2007-02-08 17.17
002108 2007-02-09 17.2
002108 2007-02-12 17.36
对num分组后,如何按时间顺序,得出后一天数据除以前一天数据的结果?