一、date_histogram函数

   histogram和date_histogram都是Bucket聚合中的常用聚合
   [ES官方文档](https://www.elastic.co/guide/index.html)
Kibana写法
GET /cars/transactions/_search {    "size" : 0,    "aggs": {       "sales": {          "date_histogram": {             "field": "sold",             "interval": "day"             "format": "yyyy-MM-dd",             "min_doc_count" : 0,             "time_zone" : "+08:00",             "extended_bounds" : {                  "min" : "2014-01-01",                 "max" : "2014-12-31"             }          }       }    } }
field ：//你的字段
interval：//日期，支持多种关键字year, quarter, month, week, day, hour, minute, second
format：//日期格式
min_doc_count：0,//这个参数强制返回空 buckets
time_zone: //时区
extended_bounds：//这个参数强制返回整年
java代码
builder.aggregation(AggregationBuilders.dateHistogram("signedAt")
         .dateHistogramInterval(DateHistogramInterval.days(1))
 .field("signedAt")
 .format("yyyy-MM-dd HH:mm:ss")
 .minDocCount(0)
 .timeZone(DateTimeZone.forID("Asia/Shanghai"))
 .offset("+8h")
//默认强制查询此日期范围
 .extendedBounds( new ExtendedBounds(DateUtil.firstDay()+" 00:00:00", DateUtil.lastDay()+" 23:59:59"))
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