ElasticSearch java API - 聚合查询

作者: carlislelee   发布时间:2016-09-20
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": {
"player": {
"properties": {
"name": {
"index": "not_analyzed",
"type": "string"
},
"age": {
"type": "integer"
},
"salary": {
"type": "integer"
},
"team": {
"index": "not_analyzed",
"type": "string"
},
"position": {
"index": "not_analyzed",
"type": "string"
}
},
"_all": {
"enabled": false
}
}
}

索引中的全部数据:

微信截图_20160920171030.png

 
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。
  • 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();
 
  • 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();
 
  • 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();

  • 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();
 
  • 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。 
  • 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);
 
  • Aggregation结果的解析/输出

得到response后:
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
}
 
  • 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。
 
如果有什么问题,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






 

3 个评论

SELECT a, sum(b) FROM TableA GROUP BY a HAVING sum(b) > 10
请问这条sql用java应该怎么写出来?
TBO_ll

TBO_ll 回复 Todo

同求,大神解决没
加一个 setPostFilter 不行吗

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