The Order Total

Now that order detail lines are being completely calculated, we wish to SUM the total of the order lines to the order total.

The SUM of Order Lines

Calculating a SUM is as easy as a FETCH. The two types of automation both depend on a foreign key. Whereas the FETCH sends information 'down' from a parent table to a child table, a SUM adds information 'up' from child rows to a parent row.

Maintaining a sum of all of the order lines is as easy as adding an automated column to the header:

column order_num:
   type_id: int
   description: Order Number
table orders_h:
   module: orders
   description: Orders
   
   column order_num:
      uisearch: "Y"
      primary_key: "Y"
      automation_id: SEQUENCE
   foreign_key customers:
      uisearch: "Y"
   
   column price_lines:
      suffix: _lines
      automation_id: SUM
      auto_formula: orders_d.price_extended

In the next tutorial we will review what we have created so far, and from there we will go on to add a credit limit constraint to our system.