Update another row value in SQL Server - sql

Question

I have a table with name, location, startdate and enddate as follows:
+------+----------+-----------+-----------+-----------+
| name | location | startdate | endate | is_active |
+------+----------+-----------+-----------+-----------+
| A | delhi | 3/26/2019 | 3/26/2019 | 1 |
| A | delhi | 3/27/2019 | 3/27/2019 | 1 |
| A | delhi | 3/28/2019 | 3/28/2019 | 1 |
| A | delhi | 3/31/2019 | 3/31/2019 | 1 |
+------+----------+-----------+-----------+-----------+
need to update like this:
+------+----------+-----------+-----------+-----------+
| name | location | startdate | endate | is_active |
+------+----------+-----------+-----------+-----------+
| A | delhi | 3/26/2019 | 3/28/2019 | 1 |
| A | delhi | 3/27/2019 | 3/27/2019 | 0 |
| A | delhi | 3/28/2019 | 3/28/2019 | 0 |
| A | delhi | 3/31/2019 | 3/31/2019 | 1 |
+------+----------+-----------+-----------+-----------+
If the startdate is consecutive, the update the end date with the end date of last consecutive startdate and also update is_active = 0 for the consecutive startdate

Answer 1

This is a gaps-and-islands problem. Here is an approach using lag() and a cumulative sum() to define the groups. The final step is conditiona logic:
select
name,
location,
startdate,
case when row_number() over(partition by name, location, grp order by startdate) = 1
then max(startdate) over(partition by name, location, grp)
else enddate
end as enddate,
case when row_number() over(partition by name, location, grp order by startdate) = 1
then 1
else 0
end as is_active
from (
select
t.*,
sum(case when startdate = dateadd(day, 1, lag_enddate) then 0 else 1 end)
over(partition by name, location order by startdate) grp
from (
select
t.*,
lag(enddate) over(partition by name, location order by startdate) lag_enddate
from mytable t
) t
) t
Demo on DB Fiddle:
name | location | startdate | enddate | is_active
:--- | :------- | :--------- | :--------- | --------:
A | delhi | 2019-03-26 | 2019-03-28 | 1
A | delhi | 2019-03-27 | 2019-03-27 | 0
A | delhi | 2019-03-28 | 2019-03-28 | 0
A | delhi | 2019-03-31 | 2019-03-31 | 1