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
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
How can this be achieved?
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
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
