====== ElasticSearch Query ======

===== From/Limit =====
  * 쿼리 결과 ''from/limit'' 지정<code json>
GET /_search
{
    "from" : 0, "size" : 10,
    "query" : {
        "term" : { "user" : "kimchy" }
    }
}
// 혹은
GET /_search?from=0&size=10
</code>

===== null 체크 =====
  * [[https://www.elastic.co/guide/en/elasticsearch/guide/current/_dealing_with_null_values.html|Dealing with Null Values | Elasticsearch: The Definitive Guide [2.x] | Elastic]]
  * 값의 존재(''IS NOT NULL'') 체크<code json>
GET /my_index/posts/_search
{
    "query" : {
        "constant_score" : {
            "filter" : {
                "exists" : { "field" : "필드이름" }
            }
        }
    }
}
</code>
  * 값이 존재하지 않음(''IS NULL'') 체크(<code json>
GET /my_index/posts/_search
{
    "query" : {
        "constant_score" : {
            "filter": {
                "missing" : { "field" : "필드이름" }
            }
        }
    }
}
</code>
===== 범위 (Range) =====
  * [[https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-range-query.html|Range Query]]<code json>
GET _search
{
    "query": {
        "range" : {
            "age" : {
                "gte" : 10, // "gt"
                "lte" : 20, // "lt"
                "boost" : 2.0
            }
        }
    }
}
</code>
  * ''gte'' : Greater-than or equal to
  * ''gt'' : Greater-than
  * ''lte'' : Less-than or equal to
  * ''lt'' : Less-than
  * ''boost'' : Sets the boost value of the query, defaults to 1.0

===== Distinct Field =====
  * [[https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-bucket-terms-aggregation.html|Terms Aggregation]]
  * ''product'' 필드값으로 distinct 하고 결과를 5개까지 출력, 이때 검색결과는 출력하지 않고 통계 결과만출력 <code json>
{
    "size": 0, // 검색결과 출력 안하게
    "aggs" : {
        "products" : {
            "terms" : {
                "field" : "product",
                "size" : 5
            }
        }
    }
}
</code>
  * 정렬하기<code json>
{
    "aggs" : {
        "genres" : {
            "terms" : {
                "field" : "genre",
                "order" : { "_count" : "asc" }  // asc/desc
            }
        }
    }
}
</code>
    * ''_term'' : 키로 정렬
    * ''_count'' : 키의 존재 갯수로 정렬
  * 필터와 함께 적용[[https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-bucket-filter-aggregation.html|Filter Aggregation]] <code json>
{
    "size": 0,
    "aggs" : {
        "t_shirts" : {
            "filter" : { "term": { "type": "t-shirt" } },
            "aggs" : {
                "avg_price" : { "avg" : { "field" : "price" } }
            }
        }
    }
}
</code>