> db.imooc_2.find({x:}).explain()

{

    "queryPlanner" : {

        "plannerVersion" : ,

        "namespace" : "test.imooc_2",

        "indexFilterSet" : false,

        "parsedQuery" : {

            "x" : {

                "$eq" :

            }

        },

        "winningPlan" : {

            "stage" : "COLLSCAN",

            "filter" : {

                "x" : {

                    "$eq" :

                }

            },

            "direction" : "forward"

        },

        "rejectedPlans" : [ ]

    },

    "serverInfo" : {

        "host" : "vnc19216859189.lan",

        "port" : ,

        "version" : "4.0.0",

        "gitVersion" : "3b07af3d4f471ae89e8186d33bbb1d5259597d51"

    },

    "ok" :

}