# SubQuery

# Rewrite EXISTS in Nested Query

OpenSearch SQL uses OpenSearch nested query to query the nested field. In OpenSearch domain, the nested query can filter the nested field based the query logic which is correspond to the [EXISTS in PartiQL](https://partiql.org/tutorial.html#use-case-checking-whether-a-nested-collection-satisfies-a-condition). It means, there could be a way to translate the EXISTS query based on the nested query.
Let’s go though the use cases find out how to translate the SQL to DSL.

## Use cases

### **1.  EXISTS**

If the SQL doesn’t have condition in the subquery, the [OpenSearch exists](https://www.elastic.co/guide/en/elasticsearch/reference/7.3/query-dsl-exists-query.html) could be used to translate the SQL to DSL.

```
SELECT e.name AS employeeName
FROM web_in AS s, s.employeesNest as e
WHERE EXISTS (SELECT * FROM e.projects AS p)

// DSL
GET /employee_nested/_search
{
  "from": 0,
  "size": 200,
  "query": {
    "bool": {
      "filter": [
        {
          "bool": {
            "must": [
              {
                "nested": {
                  "query": {
                    "exists": {
                      "field": "projects"
                    }
                  },
                  "path": "projects",
                  "ignore_unmapped": false,
                  "score_mode": "none",
                  "boost": 1
                }
              }
            ],
            "adjust_pure_negative": true,
            "boost": 1
          }
        }
      ],
      "adjust_pure_negative": true,
      "boost": 1
    }
  },
  "_source": {
    "includes": [
      "name"
    ],
    "excludes": []
  }
}

```



### **2.  EXISTS with WHERE condition**

```
// SQL
SELECT e.name AS employeeName
FROM web_in AS s, s.employeesNest as e
WHERE EXISTS(SELECT * 
             FROM e.projects AS p 
             WHERE p.name LIKE '%security%')
// DSL
{
  "from": 0,
  "size": 200,
  "query": {
    "bool": {
      "filter": [
        {
          "bool": {
            "must": [
              {
                "nested": {
                  "query": {
                    "wildcard": {
                      "projects.name": {
                        "wildcard": "security",
                        "boost": 1
                      }
                    }
                  },
                  "path": "projects",
                  "ignore_unmapped": false,
                  "score_mode": "none",
                  "boost": 1
                }
              }
            ],
            "adjust_pure_negative": true,
            "boost": 1
          }
        }
      ],
      "adjust_pure_negative": true,
      "boost": 1
    }
  },
  "_source": {
    "includes": [
      "name"
    ],
    "excludes": []
  }
}

// OpenSearch SQL
SELECT e.name 
FROM employee_nested as e, e.projects as p 
WHERE p.name LIKE 'security'

// Result
{employeeName:"Bob Smith"}
{employeeName:"Jane Smith"}
```

## Implementation
//Todo

# Appendix I - Test Data

## EmployeeName

```
{
  "employeesNest": [
    {
      "id": 3,
      "name": "Bob Smith",
      "title": null,
      "projects": [
        {
          "name": "AWS Redshift Spectrum querying",
          "started_year": 1990,
          "address": [
            {
              "city": "Seattle",
              "state": "WA"
            },
            {
              "city": "Boston",
              "state": "MA"
            }
          ]
        },
        {
          "name": "AWS Redshift security",
          "started_year": 1999,
          "address": [
            {
              "city": "Chicago",
              "state": "IL"
            }
          ]
        },
        {
          "name": "AWS Aurora security",
          "started_year": 2015
        }
      ],
      "comments": [
        {
          "date": "2018-06-23",
          "message": "I love New york",
          "likes": 56
        },
        {
          "date": "2017-10-25",
          "message": "Today is good weather",
          "likes": 22
        }
      ]
    },
    {
      "id": 4,
      "name": "Susan Smith",
      "title": "Dev Mgr",
      "projects": [],
      "comments": [
        {
          "date": "2018-06-23",
          "message": "comment_2_1",
          "likes": 56
        },
        {
          "date": "2017-10-25",
          "message": "comment_2_2",
          "likes": 22
        }
      ]
    },
    {
      "id": 6,
      "name": "Jane Smith",
      "title": "Software Eng 2",
      "projects": [
        {
          "name": "AWS Redshift security",
          "started_year": 1998
        },
        {
          "name": "AWS Hello security",
          "started_year": 2015,
          "address": [
            {
              "city": "Dallas",
              "state": "TX"
            }
          ]
        }
      ],
      "comments": [
        {
          "date": "2018-06-23",
          "message": "comment_3_1",
          "likes": 24
        },
        {
          "date": "2017-10-25",
          "message": "comment_3_2",
          "likes": 42
        }
      ]
    }
  ]
}
```