ElasticSearch 經常使用聚會查詢

以球員信息爲例，player索引的player type包含5個字段，姓名，年齡，薪水，球隊，場上位置。
index的mapping爲：

"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
        }
    }
}

索引中的所有數據：

首先，初始化Builder：

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

接下來舉例說明各類聚合操做的實現方法，由於在es的api中，多字段上的聚合操做須要用到子聚合(subAggregation)，初學者可能找不到方法（網上資料比較少，筆者在這個問題上折騰了兩天，最後度了源碼才完全搞清楚T_T），後邊會特地說明多字段聚合的實現方法。另外，聚合後的排序也會單獨說明。

• group by/count

例如要計算每一個球隊的球員數，若是使用SQL語句，應表達以下：

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多個field

例如要計算每一個球隊每一個位置的球員數，若是使用SQL語句，應表達以下：

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

例如要計算每一個球隊年齡最大/最小/總/平均的球員年齡，若是使用SQL語句，應表達以下：

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

ES的java api：

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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();

　　

 

• 對多個field求max/min/sum/avg

例如要計算每一個球隊球員的平均年齡，同時又要計算總年薪，若是使用SQL語句，應表達以下：

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

ES的java api：

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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();

　　

• 聚合後對Aggregation結果排序

例如要計算每一個球隊總年薪，並按照總年薪倒序排列，若是使用SQL語句，應表達以下：

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

ES的java api：

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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();

　　

須要特別注意的是，排序是在TermAggregation處執行的，Order.aggregation函數的第一個參數是aggregation的名字，第二個參數是boolean型，true表示正序，false表示倒序。 

• Aggregation結果條數的問題

默認狀況下，search執行後，僅返回10條聚合結果，若是想反悔更多的結果，須要在構建TermsBuilder 時指定size：

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

 

• Aggregation結果的解析/輸出

獲得response後：

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();

//球隊名

String team = buck.getKey();

//記錄數

long count = buck.getDocCount();

//獲得全部子聚合

Map subaggmap = buck.getAggregations().asMap();

//avg值獲取方法

double avg_age= ((InternalAvg) subaggmap.get("avg_age")).getValue();

//sum值獲取方法

double total_salary = ((InternalSum) subaggmap.get("total_salary")).getValue();

//...

//max/min以此類推

}

　　

• 總結

綜上，聚合操做主要是調用了SearchRequestBuilder的addAggregation方法，一般是傳入一個TermsBuilder，子聚合調用TermsBuilder的subAggregation方法，能夠添加的子聚合有TermsBuilder、SumBuilder、AvgBuilder、MaxBuilder、MinBuilder等常見的聚合操做。   從實現上來說，SearchRequestBuilder在內部保持了一個私有的 SearchSourceBuilder實例， SearchSourceBuilder內部包含一個List<AbstractAggregationBuilder>，每次調用addAggregation時會調用 SearchSourceBuilder實例，添加一個AggregationBuilder。 一樣的，TermsBuilder也在內部保持了一個List<AbstractAggregationBuilder>，調用addAggregation方法（來自父類addAggregation）時會添加一個AggregationBuilder。有興趣的讀者也能夠閱讀源碼的實現。