Question

So, I figure I could probably come up with some wacky solution, but i figure i might as well ask up front.

each user can have many orders.
each desk can have many orders.
each order has maximum 3 items in it.

trying to set things up so a user can create an order and the order auto generates a reference number and each item has a reference letter. reference number is 0-99 and loops back around to 0 once it hits 99, so orders throughout the day are easy to reference for the desks.

So, user places an order for desk #2 of 3 items:
78A: red stapler
78B: pencils
78C: a kangaroo foot

not sure if this would be done in the program logic or done at the SQL level somehow.

was thinking something like neworder = order.last + 1 and somehow tying that into a range on order create. pretty fuzzy on specifics.

Answer 1

Without knowing the answer to my comment above, I will assume you want to have the full audit stored, rather than wiping historic records; as such the 78A 78B 78C type orders are just a display format.

If you have a single Order table (containing your OrderId, UserId, DeskId, times and any other top-level stuff) and an OrderItem table (containing your OrderItemId, OrderId, LineItemId — showing 1,2 or 3 for your first and optional second and third line items in the order, and ProductId) and a Product table (ProductId, Name, Description)

then this is quite simple (thankfully) using the modulo operator, which gives the remainder of a division, allowing you in this case to count in groups of 3 and 100 (or any other number you wish).
Just do something like the following:
(you will want to join the items into a single column, I have just kept them distinct so that you can see how they work)
Obviously join/query/filter on user, desk and product tables as appropriate

select
o.OrderId,
o.UserId,
o.DeskId
o.OrderId%100 + 1 as OrderNumber, 
case when LineItem%3 = 1 then 'A'
 when LineItem%3 = 2 then 'B'
 when LineItem%3 = 0 then 'C'
end as ItemLetter,
oi.ProductId
from tb_Order o inner join tb_OrderItem oi on o.OrderId=oi.OrderId

Alternatively, you can add the itemLetter (A,B,C) and/or the OrderNumber (1-100) as computed (and persisted) columns on the tables themselves, so that they are calculated once when inserted, rather than recalculating/formatting when they are selected.
This sort-of breaks some best practice that you store the raw data in the DB and you format on retrieval; but if you are not going to update the data and you are going to select the data for more than you are going to write the data; then I would break this rule and calculate your formatting at insert time