把 Elasticsearch 当数据库使：聚合后排序

使用 https://github.com/taowen/es-monitor 可以用 SQL 进行 elasticsearch 的查询。有的时候分桶聚合之后会产生很多的桶，我们只对其中部分的桶关心。最简单的办法就是排序之后然后取前几位的结果。

ORDER BY _term

SQL

$ cat << EOF | ./es_query.py http://127.0.0.1:9200
SELECT ipo_year, COUNT(*) FROM symbol GROUP BY ipo_year ORDER BY ipo_year LIMIT 2
EOF
{"COUNT(*)": 4, "ipo_year": 1972}
{"COUNT(*)": 1, "ipo_year": 1973}

Elasticsearch

{
  "aggs": {
    "ipo_year": {
      "terms": {
        "field": "ipo_year",
        "order": [
          {
            "_term": "asc"
          }
        ],
        "size": 2
      },
      "aggs": {}
    }
  },
  "size": 0
}

因为 ipo_year 是 GROUP BY 的字段，所以按这个排序用_term指代。

{
  "hits": {
    "hits": [],
    "total": 6714,
    "max_score": 0.0
  },
  "_shards": {
    "successful": 1,
    "failed": 0,
    "total": 1
  },
  "took": 3,
  "aggregations": {
    "ipo_year": {
      "buckets": [
        {
          "key": 1972,
          "doc_count": 4
        },
        {
          "key": 1973,
          "doc_count": 1
        }
      ],
      "sum_other_doc_count": 2893,
      "doc_count_error_upper_bound": 0
    }
  },
  "timed_out": false
}

ORDER BY _count

SQL

$ cat << EOF | ./es_query.py http://127.0.0.1:9200
SELECT ipo_year, COUNT(*) AS ipo_count FROM symbol GROUP BY ipo_year ORDER BY ipo_count LIMIT 2
EOF
{"ipo_count": 1, "ipo_year": 1973}
{"ipo_count": 2, "ipo_year": 1980}

Elasticsearch

{
  "aggs": {
    "ipo_year": {
      "terms": {
        "field": "ipo_year",
        "order": [
          {
            "_count": "asc"
          }
        ],
        "size": 2
      },
      "aggs": {}
    }
  },
  "size": 0
}
{
  "hits": {
    "hits": [],
    "total": 6714,
    "max_score": 0.0
  },
  "_shards": {
    "successful": 1,
    "failed": 0,
    "total": 1
  },
  "took": 2,
  "aggregations": {
    "ipo_year": {
      "buckets": [
        {
          "key": 1973,
          "doc_count": 1
        },
        {
          "key": 1980,
          "doc_count": 2
        }
      ],
      "sum_other_doc_count": 2895,
      "doc_count_error_upper_bound": -1
    }
  },
  "timed_out": false
}

ORDER BY 指标

SQL

$ cat << EOF | ./es_query.py http://127.0.0.1:9200
    SELECT ipo_year, MAX(market_cap) AS max_market_cap FROM symbol
    GROUP BY ipo_year ORDER BY max_market_cap LIMIT 2
EOF
{"max_market_cap": 826830000.0, "ipo_year": 1982}
{"max_market_cap": 847180000.0, "ipo_year": 2016}

Elasticsearch

{
  "aggs": {
    "ipo_year": {
      "terms": {
        "field": "ipo_year",
        "order": [
          {
            "max_market_cap": "asc"
          }
        ],
        "size": 2
      },
      "aggs": {
        "max_market_cap": {
          "max": {
            "field": "market_cap"
          }
        }
      }
    }
  },
  "size": 0
}
{
  "hits": {
    "hits": [],
    "total": 6714,
    "max_score": 0.0
  },
  "_shards": {
    "successful": 1,
    "failed": 0,
    "total": 1
  },
  "took": 20,
  "aggregations": {
    "ipo_year": {
      "buckets": [
        {
          "max_market_cap": {
            "value": 826830000.0
          },
          "key": 1982,
          "doc_count": 4
        },
        {
          "max_market_cap": {
            "value": 847180000.0
          },
          "key": 2016,
          "doc_count": 6
        }
      ],
      "sum_other_doc_count": 2888,
      "doc_count_error_upper_bound": -1
    }
  },
  "timed_out": false
}

HISTOGRAM 和 ORDER BY

除了 terms aggregation，其他 aggregation 也支持 order by 但是并不完善。比如 histogram aggregation 支持 sort 但是并不支持 size （也就是可以ORDER BY 但是不能 LIMIT）。官方有计划增加一个通用的支持 LIMIT 的方式，不过还没有实现：https://github.com/elastic/elasticsearch/issues/14928

SQL

$ cat << EOF | ./es_query.py http://127.0.0.1:9200
    SELECT ipo_year_range, MAX(market_cap) AS max_market_cap FROM symbol
    GROUP BY histogram(ipo_year, 10) AS ipo_year_range ORDER BY ipo_year_range
EOF
{"ipo_year_range": 1970, "max_market_cap": 18370000000.0}
{"ipo_year_range": 1980, "max_market_cap": 522690000000.0}
{"ipo_year_range": 1990, "max_market_cap": 230940000000.0}
{"ipo_year_range": 2000, "max_market_cap": 470490000000.0}
{"ipo_year_range": 2010, "max_market_cap": 287470000000.0}

Elasticsearch

{
  "aggs": {
    "ipo_year_range": {
      "aggs": {
        "max_market_cap": {
          "max": {
            "field": "market_cap"
          }
        }
      },
      "histogram": {
        "field": "ipo_year",
        "interval": 10,
        "order": {
          "_key": "asc"
        }
      }
    }
  },
  "size": 0
}
{
  "hits": {
    "hits": [],
    "total": 6714,
    "max_score": 0.0
  },
  "_shards": {
    "successful": 1,
    "failed": 0,
    "total": 1
  },
  "took": 2,
  "aggregations": {
    "ipo_year_range": {
      "buckets": [
        {
          "max_market_cap": {
            "value": 18370000000.0
          },
          "key": 1970,
          "doc_count": 5
        },
        {
          "max_market_cap": {
            "value": 522690000000.0
          },
          "key": 1980,
          "doc_count": 155
        },
        {
          "max_market_cap": {
            "value": 230940000000.0
          },
          "key": 1990,
          "doc_count": 598
        },
        {
          "max_market_cap": {
            "value": 470490000000.0
          },
          "key": 2000,
          "doc_count": 745
        },
        {
          "max_market_cap": {
            "value": 287470000000.0
          },
          "key": 2010,
          "doc_count": 1395
        }
      ]
    }
  },
  "timed_out": false
}