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：

1. "mappings": {
2. "quote": {
3. "properties": {
4. "adj_close": {
5. "type": "long"
6. },
7. "open": {
8. "type": "long"
9. },
10. "symbol": {
11. "index": "not_analyzed",
12. "type": "string"
13. },
14. "volume": {
15. "type": "long"
16. },
17. "high": {
18. "type": "long"
19. },
20. "low": {
21. "type": "long"
22. },
23. "date": {
24. "format": "strict_date_optional_time||epoch_millis",
25. "type": "date"
26. },
27. "close": {
28. "type": "long"
29. }
30. },
31. "_all": {
32. "enabled": false
33. }
34. }
35. }

索引中的全部数据：

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：

1. TermsBuilder teamAgg= AggregationBuilders.terms("player_count ").field("team");
2. sbuilder.addAggregation(teamAgg);
3. 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：

1. TermsBuilder teamAgg= AggregationBuilders.terms("player_count ").field("team");
2. TermsBuilder posAgg= AggregationBuilders.terms("pos_count").field("position");
3. sbuilder.addAggregation(teamAgg.subAggregation(posAgg));
4. 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：

1. TermsBuilder teamAgg= AggregationBuilders.terms("player_count ").field("team");
2. MaxBuilder ageAgg= AggregationBuilders.max("max_age").field("age");
3. sbuilder.addAggregation(teamAgg.subAggregation(ageAgg));
4. 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：

1. TermsBuilder teamAgg= AggregationBuilders.terms("team");
2. AvgBuilder ageAgg= AggregationBuilders.avg("avg_age").field("age");
3. SumBuilder salaryAgg= AggregationBuilders.avg("total_salary ").field("salary");
4. sbuilder.addAggregation(teamAgg.subAggregation(ageAgg).subAggregation(salaryAgg));
5. 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：

1. TermsBuilder teamAgg= AggregationBuilders.terms("team").order(Order.aggregation("total_salary ", false);
2. SumBuilder salaryAgg= AggregationBuilders.avg("total_salary ").field("salary");
3. sbuilder.addAggregation(teamAgg.subAggregation(salaryAgg));
4. 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：

1. <span style="white-space:pre"> </span>Map<String, Aggregation> aggMap = response.getAggregations().asMap();
2. StringTerms teamAgg= (StringTerms) aggMap.get("keywordAgg");
3. Iterator<Bucket> teamBucketIt = teamAgg.getBuckets().iterator();
4. while (teamBucketIt .hasNext()) {
5. Bucket buck = teamBucketIt .next();
6. //球队名
7. String team = buck.getKey();
8. //记录数
9. long count = buck.getDocCount();
10. //得到所有子聚合
11. Map subaggmap = buck.getAggregations().asMap();
12. //avg值获取方法
13. double avg_age= ((InternalAvg) subaggmap.get("avg_age")).getValue();
14. //sum值获取方法
15. double total_salary = ((InternalSum) subaggmap.get("total_salary")).getValue();
16. //...
17. //max/min以此类推
18. }