SELECT  Registration_Date,COUNT(U.User_ID) AS amoutOfUsers
INTO #UsersPerDay
FROM Users U
GROUP BY Registration_Date

SELECT U.*,Yesterday= DATEADD(DAY, -1, U.Registration_Date)
INTO #UsersPerDayYes
FROM #UsersPerDay UA

SELECT UA. Registration_Date,UA. amoutOfUsers,
ChangeFromYesterday= CASE WHEN UB. Registration_Date IS NULL THEN 0 ELSE( UA. amoutOfUsers - UB. amoutOfUsers) END
FROM #UsersPerDayYes UA LEFT JOIN #UsersPerDayYes UB ON (UA. Yesterday= UB. Registration_Date)