In SQL server if you have columns which are of Date/Time type then sometimes you need to find their difference for passing into the application when needed.

So for doing that SQL Server provides a function called DATEDIFF, it is mainly used for finding the Date and Time difference in SQL.

-- Daywise Difference

SELECT DATEDIFF(day, GETDATE(), ExpiryDate)  FROM EMPLOYEE

We can get the difference in the terms of days years minutes hours that depends on the query  arguments passed.

-- Hours Difference

SELECT DATEDIFF( hour, GETDATE(), ExpiryDate) FROM EMPLOYEE

We can also use this function for setting the values in the SQL statement.

UPDATE NUDGE
		SET DaysTillExpire = CASE  WHEN DATEDIFF(day, GETDATE(), ExpiryDate) < 0 THEN 0
									ELSE DATEDIFF(day, GETDATE(), ExpiryDate)
							END				
		,
		HoursTillExpire = CASE  WHEN DATEDIFF( hour, GETDATE(), ExpiryDate) < 0 THEN 0
									ELSE DATEDIFF(day, GETDATE(), ExpiryDate)
							END				

		,
		IsExpired = CASE WHEN DATEDIFF(day, GETDATE(), ExpiryDate) < 0 AND DATEDIFF( hour, GETDATE(), ExpiryDate) < 0 THEN 1
							ELSE 0
							END