1. A computer implemented method, the method comprising: identifying a first set of search results responsive to a first query during a search session, each search result of the first set of search results having a corresponding ranking score, and the first set of search results being ranked according to ranking scores; identifying a second set of search results responsive to a second query during the search session, each search result of the second set of search results having a corresponding ranking score, and the second set of search results being ranked according to ranking scores, wherein the second query is different from the first query; identifying one or more repetitive search results, each of the one or more repetitive search results being a search result in both the first set of search results and the second set of search results; determining a score threshold for the second set of search results; identifying one or more candidate search results, candidate search results being repetitive search results that have a ranking score greater than the score threshold, the candidate search results comprising a first candidate search result, the first candidate search result having a ranking in the second set of search results according to the respective ranking scores of the first candidate search results; demoting the first candidate search result in the second set of search results by lowering the ranking of the first candidate search result in the second set of search results; and after demoting the first candidate search result in the second set of search results, providing the second set of search results in a response to the second query; wherein the identifying, determining, demoting and providing are performed by data processing apparatus.