SQLite virtual tables allow a developer to define the contents of a table through code. By defining a set of callback functions that fetch and return rows and columns, a developer can create a link between the SQLite data processing engine and any data source. This allows SQLite to run queries against the data source without importing the data into a standard table.
Virtual tables are an extremely useful way to generate reports or allow ad hoc queries against logs or any tabular data set. Rather than writing a set of custom search or reporting tools, the data can simply be exposed to the SQLite engine. This allows reports and queries to be expressed in SQL, a language that many developers are already familiar with using. It also enables the use of generic database visualization tools and report generators.
Chapter 10 shows how to build a virtual table module that provides direct access to live web server logs.