PUT test
{
  "mappings": {
    "properties": {
      "field1": {
        "type": "long"
      },
      "field2": {
        "type": "boolean"
      }
    }
  }
}

POST test/_bulk?refresh=true
{"index": {}}
{"field1": ["1", 1], "field2": ["true", true]}
{"index": {}}
{"field1": "1", "field2": "true"}

POST _plugins/_sql
{
  "query": "select field1, field2 from test"
}

#response
{
  "schema": [
    {
      "name": "field1",
      "type": "long"
    },
    {
      "name": "field2",
      "type": "boolean"
    }
  ],
  "datarows": [
    [
      "1",
      "true"
    ],
    [
      0,
      false
    ]
  ],
  "total": 2,
  "size": 2,
  "status": 200
}