mysql> explain format=json select clock,ns,value from history where itemid=1356876 and clock<=1457488224 and clock>1456883424\G
*************************** 1. row ***************************
EXPLAIN: {
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.41"
    },
    "table": {
      "table_name": "history",
      "partitions": [
        "p2016_03_05",
        "p2016_03_06",
        "p2016_03_07",
        "p2016_03_08",
        "p2016_03_09"
      ],
      "access_type": "range",
      "possible_keys": [
        "history_1"
      ],
      "key": "history_1",
      "used_key_parts": [
        "itemid",
        "clock"
      ],
      "key_length": "12",
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "index_condition": "((`zabbix`.`history`.`itemid` = 1356876) and (`zabbix`.`history`.`clock` <= 1457488224) and (`zabbix`.`history`.`clock` > 1456883424))",
      "cost_info": {
        "read_cost": "2.21",
        "eval_cost": "0.20",
        "prefix_cost": "2.41",
        "data_read_per_join": "32"
      },
      "used_columns": [
        "itemid",
        "clock",
        "value",
        "ns"
      ]
    }
  }
}


mysql> explain format=json select clock,ns,value from history where itemid=1356876\G
*************************** 1. row ***************************
EXPLAIN: {
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.20"
    },
    "table": {
      "table_name": "history",
      "partitions": [
        "p2016_03_05",
        "p2016_03_06",
        "p2016_03_07",
        "p2016_03_08",
        "p2016_03_09",
        "p2016_03_10",
        "p2016_03_11"
      ],
      "access_type": "ref",
      "possible_keys": [
        "history_1"
      ],
      "key": "history_1",
      "used_key_parts": [
        "itemid"
      ],
      "key_length": "8",
      "ref": [
        "const"
      ],
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "1.00",
        "eval_cost": "0.20",
        "prefix_cost": "1.20",
        "data_read_per_join": "32"
      },
      "used_columns": [
        "itemid",
        "clock",
        "value",
        "ns"
      ]
    }
  }
}
1 row in set, 1 warning (0.00 sec)