1. A computer-implemented method for approximating a number of results returned by a query over a relational data source, the method comprising: receiving, by an information processing system, a number of distinct values in each field of each relation in a relational data source, wherein the distinct values are a size approximation, and receiving, by the information processing system, a plurality of relationships between fields, where a relationship between a first field and at least a second field is a relationship approximation that approximates a number of distinct values stored in the second field for each value stored in the first field, and producing, by the information processing system based on the size approximation and the relationship approximation, a query size approximation of the number of distinct values in each field of a result of a query, and producing, by the information processing system, based on the query size approximation, a query quantity approximation of a total number of distinct records in the result of the query without running the query against the relational data source.