sql 事物造成的死锁问题怎么解决

Question

做了个程序,局域网内多个用户进行下面sql事物操作的时候容易出现死锁的情况,使得部分用户户无法插入数据,下面是简化版,大概的意思有了,请问该如何优化修改
begin transaction
declare @errorSum int
set @errorSum=0

                    if ((select 1 from Table1  where student_sn=@student_sn) = 1)
                        begin
                            update Table1 set is_chk=0   where student_sn=@student_sn;
                        end
                    else
                        begin
                            insert into Table1  (student_sn) values(@student_sn);
                        end

                    select count(1) from  Table1 where  user_sn=@user_sn

                    set @errorSum=@errorSum+@@ERROR
                    if @errorSum<>0
                        begin
                            rollback transaction
                        end
                    else
                        begin
                            commit transaction
                        end