Querying structured infomation retrieval database

Merge smaller subsets of queries first,

Given 3 sets: {1, 2}, {1, 2, 3, 4}, {1, 2, 3, 4, 5, 6}

{1, 2, 3, 4} AND {1, 2}

rather than:

{1, 2, 3, 4} AND {1, 2, 3, 4, 5, 6}