SP_User Store Procedure (JWT Auth) - ASP.NET Core Web API

 CREATE PROCEDURE [dbo].[SP_User]

@UserId varchar(50)

,@Username varchar(50)

,@Email varchar(50)

,@Password varchar(50)

,@OperationType int

AS

BEGIN TRAN

IF(@OperationType = 1) --Insert

BEGIN

IF EXISTS(SELECT * FROM [User] WHERE Username=@Username)

BEGIN

ROLLBACK

RAISERROR (N'This username already exist !!!',16,1);

RETURN

END

IF EXISTS(SELECT * FROM [User] WHERE Email=@Email)

BEGIN

ROLLBACK

RAISERROR (N'This email already exist !!!',16,1);

RETURN

END

SET @UserId = (SELECT MAX(UserId) FROM [USER]) + 1

INSERT INTO [USER] (UserId, Username, Email, [Password])

        VALUES(@UserId, @Username, @Email, @Password)

SELECT * FROM [USER] WHERE UserId=@UserId

END

ELSE IF(@OperationType = 2) --Update

BEGIN

IF (@UserId = 0)

BEGIN

ROLLBACK

RAISERROR (N'Invalid User !!!',16,1);

RETURN

END

IF EXISTS(SELECT * FROM [User] WHERE Email=@Email AND UserId!=@UserId)

BEGIN

ROLLBACK

RAISERROR (N'This email already exist !!!',16,1);

RETURN

END

UPDATE [USER] SET Username=@Username

,Email=@Email

WHERE UserId=@UserId

SELECT * FROM [USER] WHERE UserId=@UserId

END

ELSE IF(@OperationType = 3) --Delete

BEGIN

IF (@UserId = 0)

BEGIN

ROLLBACK

RAISERROR (N'Invalid User !!!',16,1);

RETURN

END

DELETE FROM [USER] WHERE UserId=@UserId

END

COMMIT TRAN