SQL calculate date difference between two columns code example

Example: how to get the date diff of 2 dates in the same fieldin sql server

WITH Partitioned AS(	SELECT *, ROW_NUMBER() OVER (PARTITION BY cu_id, date ORDER BY cu_id, date) AS RowNumber	FROM @Table) SELECT 	*,	CASE 		WHEN RowNumber > 1 THEN 0		ELSE COALESCE(DATEDIFF(DAY, (SELECT MAX(date) FROM @Table WHERE date < a.date AND cu_id = a.cu_id), a.date), 0)	END AS Days_betweenFROM Partitioned a