select min(a) from tab group by b如何在es中实现

{

  "query": {

    "bool": {

      "must": [

        {

          "match_all": {}

        }

      ]

    }

  },

  "from": 0,

  "size": 0,

  "aggregations": {

    "b": {

      "aggregations": {

        "MIN(a)": {

          "min": {

            "field": "a"

          }

        }

      },

      "terms": {

        "field": "b",

        "size": "1"

      }

    }

  }

}