SQL select，仅返回日期和时间顺序中比率或数字发生变化的结果

Question

我正在尝试返回由时间段分隔的 SQL 数据库中的费率，例如，我只需要返回费率从初始时间段发生变化的结果； BH(Bank Holiday)、WD(Weekday)、WE(Weekend)供参考...

ClientType  Column2     Column 3
Private     BH 06:00    £22.00
Private     BH 09:00    £25.00
Private     BH 17:00    £25.00
Private     WD 06:00    £12.00
Private     WD 09:00    £14.00
Private     WD 17:00    £14.00
Private     WE 06:00    £16.00
Private     WE 09:00    £16.00
Private     WE 17:00    £16.00
Family      BH 06:00    £28.00
Family      BH 09:00    £28.00
Family      BH 17:00    £28.00
Family      WD 06:00    £12.00
Family      WD 09:00    £12.00
Family      WD 17:00    £12.00
Family      WE 06:00    £15.00
Family      WE 09:00    £15.00
Family      WE 17:00    £15.00

所以试图将上述数据返回为，

ClientType  Column2     Column 3
Private     BH 06:00    £22.00
Private     BH 09:00    £25.00
Private     WD 06:00    £12.00
Private     WD 09:00    £14.00
Private     WE 06:00    £16.00
Family      BH 06:00    £28.00
Family      WD 06:00    £12.00
Family      WE 06:00    £15.00

仅在速率随时间段序列发生变化时返回结果。

此外，如果结果仅返回每个时间段之一，例如 Family 类型的客户端，那么它将将该时间段重命名为 BH、WD 和 WE。例如

ClientType  Column2     Column 3
Private     BH 06:00    £22.00
Private     BH 09:00    £25.00
Private     WD 06:00    £12.00
Private     WD 09:00    £14.00
Private     WE          £16.00
Family      BH          £28.00
Family      WD          £12.00
Family      WE          £15.00

谢谢

Answer 1

我想你可以用lag()做你想做的事：

select clienttype, column2, column3
from (select t.*,
             lag(column3) over (partition by clienttype, left(column2, 2) order by column2) as prev_column3
      from t
     ) t
where prev_column3 is null or prev_column3 <> column3;