insert语句通不过，不知那里错了

Question

VALUES里引用的区部变量都是string类形的，看起来没什么问题可就是执行不了，请求指点："Insert into Bill(BillNo,TableNo,GuestQty,BillDate,OrderDate,FinishTag,Waiter,MealSectionCode,Operator) 
Values(" + billno + "," + tableno + "," + guestQty + "," + hotelData + "," + user.Rows[rno]["time"].ToString() + ",0," + waiter + "," + mealSectionCode.ToString() + "," + user.Rows[rno]["name"].ToString() + ")");

Answer 1

"Insert   into   Bill(BillNo,TableNo,GuestQty,BillDate,OrderDate,FinishTag,Waiter,MealSectionCode,Operator)   
Values('"   +   billno   +   "','"   +   tableno   +   "','"   +   guestQty   +   "','"   +   hotelData   +   "','"   +   user.Rows[rno]["time"].ToString()   +   "','0','"   +   waiter   +   "','"   +   mealSectionCode.ToString()   +   "','"   +   user.Rows[rno]["name"].ToString()   +   "')");