1. A method for generating a query results preview, the method comprising: receiving a preliminary query while a query for a search is being constructed; determining, using a processor, a distribution of result items that would be retrieved if the search were executed using the preliminary query, among a new result category comprising new result items and a previous result category comprising result items previously retrieved in a session; generating the query results preview using the distribution of result items that would be retrieved if the search were executed using the preliminary query; and providing the query results preview while the query for the search is being constructed and prior to execution of the search using the query.