When system runs a report, a proper database query is executed. This query is written in a
language called HQL (Hibernate Query Language), and you should know its basics when altering
a report. Fortunately, most reports are defined with very simple HQL statements, and one can
catch up quickly by analyzing built-in reports. Alternatively, here is a link to quite reasonable HQL
manual. To alter a report, you also must be familiar with application`s database structure
described here.
Each report can contain report parameters. Report parameter is an extra condition added to
query if user wishes to constraint it more. For example, imagine the following report: show me all
jobs. The extra parameter may be, for example, customer name. If user enters customer name,
the report will return only jobs for selected customer.