CREATE TRIGGER tr_levelRestriction ON UserGameItems
FOR INSERT
AS
     DECLARE @UserLevel INT=
     (
         SELECT ug.[Level]
         FROM inserted AS ugi
              JOIN UsersGames AS ug ON ugi.UserGameId = ug.Id
     );
     DECLARE @ItemLevel INT=
     (
         SELECT i.MinLevel
         FROM inserted AS ugi
              JOIN Items AS i ON ugi.ItemId = i.Id
     );
     IF @UserLevel < @ItemLevel
         BEGIN
             ROLLBACK;
             RAISERROR('User level is too low for this item!', 16, 1);
             RETURN;
     END;

     INSERT INTO UserGameItems
            SELECT *
            FROM inserted;