合并数据库中重复的时间记录 [英] Merge duplicate temporal records in database

问题描述

我有一个时态数据库表，其中一些数据是重复的.

I have a temporal database table where some of the data is duplicated.

EmployeeId   StartDate   EndDate     Column1   Column2
1000         2009/05/01  2010/04/30   X         Y
1000         2010/05/01  2011/04/30   X         Y
1000         2011/05/01  2012/04/30   X         X
1000         2012/05/01  2013/04/30   X         Y
1000         2013/05/01  NULL         X         X

如上所示，有些行是冗余的，可以合并为一行，而不会违反数据有效性.我想尽可能合并这些行，结果应该是这样的

As seen above there are some rows which are redundant and can be merged to form a single row without violating the data validity. I want to merge such rows wherever possible and the result should look like this

EmployeeId   StartDate   EndDate     Column1   Column2
1000         2009/05/01  2011/04/30   X         Y
1000         2011/05/01  2012/04/30   X         X
1000         2012/05/01  2013/04/30   X         Y
1000         2013/05/01  NULL         X         X

如何实现?

推荐答案

试试这个，如果你能确保所有的开始日期和结束日期都是连续的:

Try this if you can ensure that all the start date and end date are continuous :

with  t1 as  --tag first row with 1 in a continuous time series
(
select t1.*, case when t1.column1=t2.column1 and t1.column2=t2.column2
                  then 0 else 1 end as tag
  from your_table t1
  left join your_table t2
    on t1.EmployeeId= t2.EmployeeId and dateadd(day,-1,t1.StartDate)= t2.EndDate
)
select t1.EmployeeId, t1.StartDate, 
       case when min(T2.StartDate) is null then null
            else dateadd(day,-1,min(T2.StartDate)) end as EndDate,
       t1.Column1, t1.Column2
  from (select t1.* from t1 where tag=1 ) as t1  -- to get StartDate
  left join (select t1.* from t1 where tag=1 ) as t2  -- to get a new EndDate
    on t1.EmployeeId= t2.EmployeeId and t1.StartDate < t2.StartDate
 group by t1.EmployeeId, t1.StartDate, t1.Column1,   t1.Column2

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