Elasticsearch SQL 访问

它是一个组件，允许针对 Elasticsearch 实时执行类似 SQL 的查询。 我们可以将 Elasticsearch SQL 视为翻译器，它既理解 SQL 又理解 Elasticsearch，并且可以通过利用 Elasticsearch 功能轻松地实时、大规模地读取和处理数据。

Elasticsearch SQL 的优势

• 它具有本机集成 - 根据底层存储对相关节点有效地执行每个查询。
• 没有外部部件 - 不需要额外的硬件、进程、运行时或库来查询 Elasticsearch。
• 轻量级和高效 - 它包含并公开 SQL 以允许实时进行适当的全文搜索。

示例

PUT /schoollist/_bulk?refresh
   {"index":{"_id": "CBSE"}}
   {"name": "GleanDale", "Address": "JR. Court Lane", "start_date": "2011-06-02",
   "student_count": 561}
   {"index":{"_id": "ICSE"}}
   {"name": "Top-Notch", "Address": "Gachibowli Main Road", "start_date": "1989-
   05-26", "student_count": 482}
   {"index":{"_id": "State Board"}}
   {"name": "Sunshine", "Address": "Main Street", "start_date": "1965-06-01",
   "student_count": 604}

运行上面的代码，我们得到如下所示的响应

{
   "took" : 277,
   "errors" : false,
   "items" : [
      {
         "index" : {
            "_index" : "schoollist",
            "_type" : "_doc",
            "_id" : "CBSE",
            "_version" : 1,
            "result" : "created",
            "forced_refresh" : true,
            "_shards" : {
               "total" : 2,
               "successful" : 1,
               "failed" : 0
            },
            "_seq_no" : 0,
            "_primary_term" : 1,
            "status" : 201
         }
      },
      {
         "index" : {
            "_index" : "schoollist",
            "_type" : "_doc",
            "_id" : "ICSE",
            "_version" : 1,
            "result" : "created",
            "forced_refresh" : true,
            "_shards" : {
               "total" : 2,
               "successful" : 1,
               "failed" : 0
            },
            "_seq_no" : 1,
            "_primary_term" : 1,
            "status" : 201
         }
      },
      {
         "index" : {
            "_index" : "schoollist",
            "_type" : "_doc",
            "_id" : "State Board",
            "_version" : 1,
            "result" : "created",
            "forced_refresh" : true,
            "_shards" : {
               "total" : 2,
               "successful" : 1,
               "failed" : 0
            },
            "_seq_no" : 2,
            "_primary_term" : 1,
            "status" : 201
         }
      }
   ]
}

SQL 查询

以下示例显示了我们如何构建 SQL 查询

POST /_sql?format=txt
{
   "query": "SELECT * FROM schoollist WHERE start_date < '2000-01-01'"
}

运行上面的代码，我们得到如下所示的响应

Address             | name          | start_date             | student_count
--------------------+---------------+------------------------+---------------
Gachibowli Main Road|Top-Notch      |1989-05-26T00:00:00.000Z|482
Main Street         |Sunshine       |1965-06-01T00:00:00.000Z|604

注意 - 通过更改上面的 SQL 查询，我们可以获得不同的结果集。