A Graphical Query Front End system for Querying a relational database displays the elements of a Query in graphical form. The graphical query consists of tables, shown as nodes on a display, used as input (i.e. connected) to operator nodes, which produce output tables by modifying the inputs based on information provided by the user. There are several operators, each of which represents a different piece of defining a query, e.g. selecting columns or selecting rows. These operator nodes may then be used as inputs to operator nodes which modify their inputs to produce output tables, and so on until the desired result is achieved.