ConstantScoreQuery的定义：
A query that wraps another query and simply returns a constant score equal to 1 for every document that matches the query. It therefore simply strips of all scores and always returns 1.
结合DisMaxQueryBuilder可以查找所有 匹配上(分数为1)的若干doc，
没匹配上(分数为0)的若干doc不返回。