ElasticSearch java API - 聚合查询

以球员信息为例，player索引的player type包含5个字段，姓名，年龄，薪水，球队，场上位置。

index的mapping为：

"mappings": {"quote": {"properties": {"adj_close": {"type": "long"},"open": {"type": "long"},"symbol": {"index": "not_analyzed","type": "string"},"volume": {"type": "long"},"high": {"type": "long"},"low": {"type": "long"},"date": {"format": "strict_date_optional_time||epoch_millis","type": "date"},"close": {"type": "long"}},"_all": {"enabled": false}}}

索引中的全部数据：

nameagesalaryteampositionjames333000cavsfirving252000cavpgcurry291000warpgthompson262000warsggreen262000warpfgarnett401000timpftowns21500timclavin21300timsgwigins20500timsf

首先，初始化Builder：

SearchRequestBuilder sbuilder = client.prepareSearch("player").setTypes("player");

接下来举例说明各种聚合操作的实现方法，因为在es的api中，多字段上的聚合操作需要用到子聚合(subAggregation)，初学者可能找不到方法（网上资料比较少，笔者在这个问题上折腾了两天，最后度了源码才彻底搞清楚T_T），后边会特意说明多字段聚合的实现方法。另外，聚合后的排序也会单独说明。

1. group by/count

例如要计算每个球队的球员数，如果使用SQL语句，应表达如下：

select team, count(*) as player_count from player group by team;

ES的java api：

TermsBuilder teamAgg= AggregationBuilders.terms("player_count ").field("team");sbuilder.addAggregation(teamAgg);SearchResponse response = sbuilder.execute().actionGet();

2.group by多个field

例如要计算每个球队每个位置的球员数，如果使用SQL语句，应表达如下：

select team, position, count(*) as pos_count from player group by team, position;

ES的java api：

TermsBuilder teamAgg= AggregationBuilders.terms("player_count ").field("team");TermsBuilder posAgg= AggregationBuilders.terms("pos_count").field("position");sbuilder.addAggregation(teamAgg.subAggregation(posAgg));SearchResponse response = sbuilder.execute().actionGet();

3.max/min/sum/avg

例如要计算每个球队年龄最大/最小/总/平均的球员年龄，如果使用SQL语句，应表达如下：

select team, max(age) as max_age from player group by team;

ES的java api：

TermsBuilder teamAgg= AggregationBuilders.terms("player_count ").field("team");MaxBuilder ageAgg= AggregationBuilders.max("max_age").field("age");sbuilder.addAggregation(teamAgg.subAggregation(ageAgg));SearchResponse response = sbuilder.execute().actionGet();

4.对多个field求max/min/sum/avg

例如要计算每个球队球员的平均年龄，同时又要计算总年薪，如果使用SQL语句，应表达如下：

select team, avg(age)as avg_age, sum(salary) as total_salary from player group by team;

ES的java api：

TermsBuilder teamAgg= AggregationBuilders.terms("team");AvgBuilder ageAgg= AggregationBuilders.avg("avg_age").field("age");SumBuilder salaryAgg= AggregationBuilders.avg("total_salary ").field("salary");sbuilder.addAggregation(teamAgg.subAggregation(ageAgg).subAggregation(salaryAgg));SearchResponse response = sbuilder.execute().actionGet();

5.聚合后对Aggregation结果排序

例如要计算每个球队总年薪，并按照总年薪倒序排列，如果使用SQL语句，应表达如下：

select team, sum(salary) as total_salary from player group by team order by total_salary desc;

ES的java api：

TermsBuilder teamAgg= AggregationBuilders.terms("team").order(Order.aggregation("total_salary ", false);SumBuilder salaryAgg= AggregationBuilders.avg("total_salary ").field("salary");sbuilder.addAggregation(teamAgg.subAggregation(salaryAgg));SearchResponse response = sbuilder.execute().actionGet();

需要特别注意的是，排序是在TermAggregation处执行的，Order.aggregation函数的第一个参数是aggregation的名字，第二个参数是boolean型，true表示正序，false表示倒序。

6.Aggregation结果条数的问题

默认情况下，search执行后，仅返回10条聚合结果，如果想反悔更多的结果，需要在构建TermsBuilder 时指定size：

TermsBuilder teamAgg= AggregationBuilders.terms("team").size(15);

7.Aggregation结果的解析/输出

得到response后：

<span style="white-space:pre"></span>Map<String, Aggregation> aggMap = response.getAggregations().asMap();        StringTerms teamAgg= (StringTerms) aggMap.get("keywordAgg");        Iterator<Bucket> teamBucketIt = teamAgg.getBuckets().iterator();        while (teamBucketIt .hasNext()) {            Bucket buck = teamBucketIt .next();            //球队名            String team = buck.getKey();            //记录数            long count = buck.getDocCount();            //得到所有子聚合            Map subaggmap = buck.getAggregations().asMap();            //avg值获取方法            double avg_age= ((InternalAvg) subaggmap.get("avg_age")).getValue();            //sum值获取方法            double total_salary = ((InternalSum) subaggmap.get("total_salary")).getValue();            //...            //max/min以此类推        }

8. 总结

综上，聚合操作主要是调用了SearchRequestBuilder的addAggregation方法，通常是传入一个TermsBuilder，子聚合调用TermsBuilder的subAggregation方法，可以添加的子聚合有TermsBuilder、SumBuilder、AvgBuilder、MaxBuilder、MinBuilder等常见的聚合操作。

从实现上来讲，SearchRequestBuilder在内部保持了一个私有的 SearchSourceBuilder实例， SearchSourceBuilder内部包含一个List<AbstractAggregationBuilder>，每次调用addAggregation时会调用 SearchSourceBuilder实例，添加一个AggregationBuilder。

同样的，TermsBuilder也在内部保持了一个List<AbstractAggregationBuilder>，调用addAggregation方法（来自父类addAggregation）时会添加一个AggregationBuilder。有兴趣的读者也可以阅读源码的实现。

如果有任何问题，欢迎一起讨论，如果文中有什么错误，欢迎批评指正。

注：文中使用的Elastic Search API版本为2.3.2