Example: Adding a Computed Column

When viewing Scheduled Tours, front office staff should be able to assess available places immediately by comparing the capacity (total number of available places) and the number of places already booked.

The Scheduled Tours info window should have an extra query column showing the total number of participants already enrolled for that Scheduled Tour.

To add a computed column that shows the number of participants for that scheduled tour:

1.	Open the Scheduled Tours info window.

2.	Give this info window an Extra Query. From the menu bar, choose Insert, Extra Query.

You will notice that USoft Developer automatically creates a new column in the info window to catch the results of the extra query.

3.	Navigate to the new Extra Query object. Use the Object tree, or from the menu bar, choose Design, Extra Query.

4.	Set the SQL Statement property to:

SELECT count('x')

FROM participant p, reservation r, schedtour s

WHERE s.schedtour_id = r.schedtour_id

AND r.res_id = p.res_id

5.	Test the new functionality by running the window. If it is satisfactory, save your work.

6.	Enhance the interface by changing the prompt of the extra query column to Booked, and by placing it right below the Capacity field (MAX_PART column).