Chapter 23.5, Problem 12SC

Explanation of Solution

Query for displaying the amount due:

In the given program, the amount due can be displayed in two ways:

• Compute using loop for displaying line items.
• Else, issue a query for displaying line items.

The below SQL query is used to compute and display the line items amount due:

/* Display the amount due of line items */

SELECT SUM (Product.Price * LineItem.Quantity)

FROM Product, LineItem

WHERE Product.Product_Code = LineItem.Product_Code

AND LineItem.Invoice_Number = ?

Explanation:

• The above “SELECT” statement calculates and displays the “SUM(Product.Price * LineItem.Quantity)” columns from the “Product and LineItem” tables where “Product.Product_Code” is equal to “LineItem.Product_code”  and “LineItem.Product_Code” is equal to “?”.
  • “SUM(Product.Price * LineItem.Quantity)” – It  finds and displays the total line items amount due  related to the invoice number.
    • “SUM” – It is a function used to calculate the sum of a field.
    • “Product...