请问这样的触发器怎样写？

简单例子 -


Create TRIGGER Checking_TypeCode   ON  table_a   AFTER INSERT
AS
    if not exists    (
                    select  *      
                    from    inserted i  join table_b b on i.ID = b.ID
                                        join table_c c on b.TypeID = c.TypeID   
                    where  substring(i.code, 1, 2) = c.TypeCode
                    )
    rollback