GET /my_index/posts/_search
{
    "query" : {
        "constant_score" : {
            "filter" : {
                "exists" : { "field" : "필드이름" }
            }
        }
    }
}

GET /my_index/posts/_search
{
    "query" : {
        "constant_score" : {
            "filter": {
                "missing" : { "field" : "필드이름" }
            }
        }
    }
}

{
    "size": 0,
    "aggs" : {
        "t_shirts" : {
            "filter" : { "term": { "type": "t-shirt" } },
            "aggs" : {
                "avg_price" : { "avg" : { "field" : "price" } }
            }
        }
    }
}