Elasticsearch雖然定位為Search Engine，但是因其可以持久化資料，很多時候，我們把Elasticsearch當成Database用，但是Elasticsearch不支援SQL，就需要把SQL邏輯轉換成程式碼實現對應的功能。

以下列舉了一些常用的SQL轉換成對應的Java程式碼。

1.按某個field group by查詢count

SELECT  
fieldA, COUNT(fieldA)
from table   
WHERE fieldC = "hoge" 
AND fieldD = "huga" 
AND fieldB > 10
AND fieldB <
 
 100 
group by fieldA;

對應的java code:

SearchRequestBuilder searchReq = client.prepareSearch("sample_index");
searchReq.setTypes("sample_types");
TermsBuilder termsb = AggregationBuilders.terms("my_fieldA").field("fieldA").size(100);

BoolFilterBuilder bf = FilterBuilders.boolFilter();
TermFilterBuilder tf_fieldC 
 
= FilterBuilders.termFilter("fieldC","hoge");
TermFilterBuilder tf_fieldD = FilterBuilders.termFilter("fieldD","huga");
bf.must(tf_fieldC);
bf.must(tf_fieldD);

RangeFilterBuilder rangefieldBFilter = FilterBuilders.rangeFilter("fieldB")
                .gt(10)
                .lt(100);

searchReq.setQuery(QueryBuilders.filteredQuery(QueryBuilders.matchAllQuery(),
                    FilterBuilders.andFilter(bf, rangefieldBFilter))).addAggregation(
                    termsb);
SearchResponse searchRes 
 
= searchReq.execute().actionGet();

Terms fieldATerms = searchRes.getAggregations().get("my_fieldA");
for (Terms.Bucket filedABucket : fieldATerms.getBuckets()) {
    //fieldA
    String fieldAValue = filedABucket.getKey();
    
    //COUNT(fieldA)
    long fieldACount = filedABucket.getDocCount();
}

2. 按某個field 和 date group by 並查詢另一個filed的sum，時間統計圖，時間間隔是1天。

SELECT  
DATE(create_at), fieldA, SUM(fieldB) 
from table   
group by DATE(create_at), fieldA;

對應的java code:

SearchRequestBuilder searchReq = client.prepareSearch("sample_index");
searchReq.setTypes("sample_types");
DateHistogramBuilder dhb = AggregationBuilders.dateHistogram("my_datehistogram").field("create_at").interval(DateHistogram.Interval.days(1));
TermsBuilder termsb_fa = AggregationBuilders.terms("my_fieldA").field("fieldA").size(100);
termsb_fa.subAggregation(AggregationBuilders.sum("my_sum_fieldB").field("fieldB"));
dhb.subAggregation(termsb_fa)

searchReq.setQuery(QueryBuilders.matchAllQuery()).addAggregation(dhb);
SearchResponse searchRes = searchReq.execute().actionGet();

DateHistogram dateHist = searchRes.getAggregations().get("my_datehistogram");
for (DateHistogram.Bucket dateBucket : dateHist.getBuckets()) {
    //DATE(create_at)
    String create_at = dateentry.getKey();
    Terms fieldATerms = dateBucket.getAggregations().get("my_fieldA");
    for (Terms.Bucket filedABucket : fieldATerms.getBuckets()) {
        //fieldA
        String fieldAValue = filedABucket.getKey();
        
        //SUM(fieldB)
        Sum sumagg = filedABucket.getAggregations().get("my_sum_fieldB");
        long sumFieldB = (long)sumagg.getValues();
    }
}

3. 按兩個field group by並查詢第三個filed的sum

SELECT  
fieldA, fieldC, SUM(fieldB)
from table   
group by fieldA, fieldC;

對應的java code:

SearchRequestBuilder searchReq = client.prepareSearch("sample_index");
searchReq.setTypes("sample_types");

TermsBuilder termsb_fa = AggregationBuilders.terms("my_fieldA").field("fieldA").size(100);
TermsBuilder termsb_fc = AggregationBuilders.terms("my_fieldC").field("fieldC").size(50);

termsb_fc.subAggregation(AggregationBuilders.sum("my_sum_fieldB").field("fieldB"));
termsb_fa.subAggregation(termsb_fc)

searchReq.setQuery(QueryBuilders.matchAllQuery()).addAggregation(termsb_fa);
SearchResponse searchRes = searchReq.execute().actionGet();

Terms fieldATerms = searchRes.getAggregations().get("my_fieldA");
for (Terms.Bucket filedABucket : fieldATerms.getBuckets()) {
    //fieldA
    String fieldAValue = filedABucket.getKey();
    Terms fieldCTerms = filedABucket.getAggregations().get("my_fieldC");
    for (Terms.Bucket filedCBucket : fieldCTerms.getBuckets()) {
        //fieldC
        String fieldCValue = filedCBucket.getKey();
        
        //SUM(fieldB)
        Sum sumagg = filedCBucket.getAggregations().get("my_sum_fieldB");
        long sumFieldB = (long)sumagg.getValues();
    }
}

4. 按某個filed group by 並查詢count、sum 和 average

SELECT  
fieldA, COUNT(fieldA), SUM(fieldB), AVG(fieldB) 
from table   
group by fieldA;

對應的java code:

SearchRequestBuilder searchReq = client.prepareSearch("sample_index");
searchReq.setTypes("sample_types");

TermsBuilder termsb = AggregationBuilders.terms("my_fieldA").field("fieldA").size(100);
termsb.subAggregation(AggregationBuilders.sum("my_sum_fieldB").field("fieldB"));
termsb.subAggregation(AggregationBuilders.avg("my_avg_fieldB").field("fieldB"));

searchReq.setQuery(QueryBuilders.matchAllQuery()).addAggregation(termsb);
SearchResponse searchRes = searchReq.execute().actionGet();
Terms fieldATerms = searchRes.getAggregations().get("my_fieldA");
for (Terms.Bucket filedABucket : fieldATerms.getBuckets()) {
    //fieldA
    String fieldAValue = filedABucket.getKey();
    
    //COUNT(fieldA)
    long fieldACount = filedABucket.getDocCount();
    
    //SUM(fieldB)
    Sum sumagg = filedABucket.getAggregations().get("my_sum_fieldB");
    long sumFieldB = (long)sumagg.getValues();
    
    //AVG(fieldB)
    Avg avgagg = filedABucket.getAggregations().get("my_avg_fieldB");
    double avgFieldB = avgagg.getValues();
}

5. 按某個field group by 並按另一個filed的Sum排序，獲取前10

SELECT  
fieldA, SUM(fieldB)
from table
WHERE fieldC = "hoge" 
group by fieldA
order by SUM(fieldB) DESC
limit 10;

對應的java code:

QueryBuilder termsc = QueryBuilders.termQuery("fieldC","hoge");
QueryBuilder queryBuilder = QueryBuilders.boolQuery().must(termsc);
TermsAggregationBuilder aggregationBuilder = AggregationBuilders.terms("my_fieldA").field("fieldA").size(10);
aggregationBuilder.subAggregation(AggregationBuilders.sum("my_sum_fieldB").field("fieldB"));
aggregationBuilder.order(Order.aggregation("my_sum_fieldB", false));
SearchResponse searchResponse = client.prepareSearch("sample_index").setQuery(queryBuilder).addAggregation(aggregationBuilder).execute().actionGet();
Terms terms = searchResponse.getAggregations().get("my_fieldA");
for (Terms.Bucket entry : terms.getBuckets()) {
    String fieldAValue = entry.getKey().toString();

    Sum sumagg = entry.getAggregations().get("my_sum_fieldB");
    double fieldValue = sumagg.getValue();
}