A query generator for generating a query for retrieving a desired set of data from a relational database is disclosed. The query generator is adapted to: a) receive an input query adapted to retrieve a superset of the desired set of data from the database; b) analyse a default filters table comprising one or more filter application criteria, each associated with a default filter condition that refers to data contained in the superset of data; and c) for each filter application criterion that is satisfied, modify the input query in accordance with the associated default filter condition to produce an output query adapted to retrieve the desired set of data only.