Question

有人会帮我介绍如何使用基本SQL添加组列吗？我使用Teradata SQL Assistant。

我的数据集是这样的：

mydate      color     mytime
----------------------------
9/1/2017    red        1:00
9/1/2017    red        2:00
9/1/2017    red        3:00
9/1/2017    red        4:00
9/1/2017    yellow     5:00
9/1/2017    yellow     6:00
9/1/2017    red        7:00
9/1/2017    red        8:00
9/1/2017    yellow     9:00
9/1/2017    yellow    10:00
9/1/2017    yellow    11:00
9/1/2017    yellow    12:00
9/1/2017    red       13:00
9/1/2017    red       14:00
9/1/2017    red       15:00
9/1/2017    yellow    16:00
9/1/2017    yellow    17:00

我想要的结果（添加专栏＆＃34; mygroup＆＃34;）：

mydate      color  mygroup  mytime
----------------------------------
9/1/2017    red      1      1:00
9/1/2017    red      1      2:00
9/1/2017    red      1      3:00
9/1/2017    red      1      4:00
9/1/2017    yellow   2      5:00
9/1/2017    yellow   2      6:00
9/1/2017    red      3      7:00
9/1/2017    red      3      8:00
9/1/2017    yellow   4      9:00
9/1/2017    yellow   4     10:00
9/1/2017    yellow   4     11:00
9/1/2017    yellow   4     12:00
9/1/2017    red      5     13:00
9/1/2017    red      5     14:00
9/1/2017    red      5     15:00
9/1/2017    yellow   6     16:00
9/1/2017    yellow   6     17:00

Answer 1

select
   mydate
  ,color 
  ,mytime
   -- then create the group number
  ,sum(flag)
   over (order by mydate, mytime 
         rows unbounded preceding) as mygroup
from
 ( 
    select
       mydate
      ,color 
      ,mytime
      -- first: find the row where the color changes
      -- previous row is different from current row
      ,case when min(color)
                 over (order by mydate, mytime 
                       rows between 1 preceding and 1 preceding) = color 
            then 0
            else 1
       end as flag
    from mytable
 ) as dt

MIN(color)计算是LAG函数的仿真，在TD16.10之前Teradata中没有这种函数。

使用基本SQL排名组

1 个答案: