Project: Incorporating aggregate functions

Building support for aggregate functions into our web application requires some revision of code that we have already written. As shown in this chapter, all aggregate functions work with the SELECT keyword. We will thus need to change how we support that kind of query. By the end of this section, we will build the following functionality into the web application:

• Support for all calculating functions

• Support for use of DISTINCT in conjunction with calculating functions

• Allowance for sorting using either ORDER BY or GROUP BY

• Return results in a tabular format

The order of development when revising a project should be inside out. Revise the relevant function and develop outward, through the main() function. After we code the initial variable assignments, we can then move on to revise the web interface to support the new functionality. The virtue of this process is that we do not introduce variables without support—to do so would seed security and stability...