CREATE TRIGGER Trigger_User
    ON dbo.User
    FOR UPDATE, DELETE
AS
IF UPDATE(UserName)
    BEGIN
        DECLARE @userNameBeforeUpdate NVARCHAR(255)
        DECLARE @userNameAfterUpdate NVARCHAR(255)

        SELECT @userNameBeforeUpdate = UserName FROM DELETED
        SELECT @userNameAfterUpdate = UserName FROM INSERTED
    END
ELSE IF NOT EXISTS(SELECT * FROM INSERTED)
    BEGIN
        DECLARE @userName NVARCHAR(255)

        SELECT @userName = UserName FROM DELETED
    END