Interface for extendable query objects.
"Extenders" follow the "Decorator" OOP design pattern. That is, they wrap and "decorate" another object. In our case, they implement the same interface as select queries and wrap a select query, to which they delegate almost all operations. Subclasses of this class may implement additional methods or override existing methods as appropriate. Extenders may also wrap other extender objects, allowing for arbitrarily complex "enhanced" queries.
- interface QueryExtendableInterface
database/ select.inc, line 19