ElasticSearch SQL 访问

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  SQL 访问

  它是允许对 Elasticsearch 实时执行类似SQL的查询的组件。您可以将Elasticsearch SQL视为一种翻译器，它既可以理解SQL又可以使用Elasticsearch，并且可以利用Elasticsearch功能轻松地进行大规模实时读取和处理数据。
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  Elasticsearch SQL的优点

  • 它具有本机集成-根据基础存储，对相关节点高效地执行每个查询。
  • 无需外部零件-无需额外的硬件，流程，运行时或库即可查询Elasticsearch。
  • 轻巧高效-它包含并公开了SQL，可以实时进行适当的全文本搜索。

  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}
  
  

  运行上面的代码后，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
           }
        }
     ]
  }
  

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  SQL查询

  以下示例显示了如何构建SQL查询-

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

  运行上面的代码后，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，您可以获得不同的结果集。