Subtract start date from the end date of the row before - SQL

Question

I'm not able to subtract from the start date the end date of the row above (like in the image) to create a column where I can see if there has been gaps of time between rows.

Answer 1

You can try

select *, datediff(days,lag(cast(end_date as date),1) 
over(partition by client,unique_id order by end_date),
cast(start_date as date)) 
as day_gap
from tablename
 

The datediff function will vary depending on the dialect of SQL you're using. You can check the syntax online for that particular dialect