A query generator for generating a query which retrieves a desired set of data from a relational database and performs one or more aggregation functions on the set of data is disclosed. The query generator is adapted to: a) receive user input indicating the desired set of data and the aggregation functions to be performed; b) identify each join subgraph for the desired set of data; c) for each join subgraph identified in step (b), generate an inline view which, on execution, performs all of the aggregation functions that refer only to data within that join subgraph; and d) generate an output query comprising the inline views generated in step (c) as arguments of a join.