Merge duplicate temporal records in database

Question

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

EmployeeId   StartDate   EndDate     Column1   Column2
1000         2009/05/01  2010/0         


        

Answer 1

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

Answer 2

Try this

SELECT A.EmployeeId,A.StartDate,A.EndDate,A.Column1,A.Column2 FROM (SELECT EmployeeId,StartDate,EndDate,Column1,Column2 FROM TEMP GROUP BY EmployeeId,StartDate,EndDate,Column1,Column2)A
JOIN 
(SELECT Y.EmployeeId,Y.StartDate,Y.EndDate,Y.Column1,Y.Column2 FROM TEMP X JOIN TEMP Y ON X.EmployeeId=Y.EmployeeId AND DATEADD(day,1,X.EndDate)=Y.StartDate)B 
ON A.EndDate=DATEADD(day,-1,B.StartDate)

Note: TEMP is the table with mentioned columns