如何根据elasticsearch中存储的字段值获取前5个文档？

Question

Example - test scores of one subject of students are stored in Elastic search index. Now I want to find top 5 students who scored highest in that subject.

Answer 1

Let me show it by using the example, But the first understand the concept.

First query based on the given subject, in my example famous math subject :) and then it will fetch all the students, having math subject, after that sort in desc order based in their score and then size param restricted the result to top k students.

Imp links related to answer:

https://www.elastic.co/guide/en/elasticsearch/reference/6.8/search-request-from-size.html

https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-term-query.html

https://www.elastic.co/guide/en/elasticsearch/reference/6.8/search-request-sort.html

Create an index

{
    "mappings": {
        "properties": {
            "sid": {
                "type": "integer"
            },
            "subject" :{
                "type" : "keyword"
            },
            "score" :{
                "type" : "integer"
            }
        }
    }
}

Index some docs

{
   "sid" : 1,
   "subject" :"math",
   "score" : 50
}

{
   "sid" : 2,
   "subject" :"math",
   "score" : 60
}
{
   "sid" : 3,
   "subject" :"math",
   "score" : 70
}
{
   "sid" : 4,
   "subject" :"math",
   "score" : 90
}
{
   "sid" : 5,
   "subject" :"math",
   "score" : 99
}

{
   "sid" : 6,
   "subject" :"math",
   "score" : 100
}

Search query to search on subject and sort results based on marks and return top 3 students.

{
    "sort": [
        {
            "score": {
                "order": "desc" --> define sort order
            }
        }
    ],
    "query": {
        "term": {
            "subject": "math"
        }
    },
    "size":3 -->important, you can change it to fetch top K students, Just change 3 to whatever no you want to fetch.
}

Search query result

{
            "_index": "leaderboard",
            "_type": "_doc",
            "_id": "5",
            "_score": null,
            "_source": {
               "sid": 6,
               "subject": "math",
               "score": 100
            },
            "sort": [
               100
            ]
         },
         {
            "_index": "leaderboard",
            "_type": "_doc",
            "_id": "4",
            "_score": null,
            "_source": {
               "sid": 4,
               "subject": "math",
               "score": 90
            },
            "sort": [
               90
            ]
         },
         {
            "_index": "leaderboard",
            "_type": "_doc",
            "_id": "3",
            "_score": null,
            "_source": {
               "sid": 3,
               "subject": "math",
               "score": 70
            },
            "sort": [
               70
            ]
         }

Answer 2

Simply sort searched results by the field you want ie score
This doc may help you https://www.elastic.co/guide/en/elasticsearch/reference/6.8/search-request-sort.html