Optimizer trace prints date in hexadecimal

create table t1 (start_date date, end_date date, filler char(100), key(start_date, end_date)) ;

insert into t1 select date_add(now(), interval a day), date_add(now(), interval (a+7) day), 'data' from one_k;

Query OK, 1000 rows affected, 2000 warnings (0.40 sec)

Records: 1000  Duplicates: 0  Warnings: 2000

mysql> set optimizer_trace=1;

mysql> explain format=json select * from t1 force index(start_date) where start_date >= '2019-02-10' and end_date <'2019-04-01';

| {

  "query_block": {

    "select_id": 1,

    "table": {

      "table_name": "t1",

      "access_type": "range",

      "possible_keys": ["start_date"],

      "key": "start_date",

      "key_length": "8",

      "used_key_parts": ["start_date", "end_date"],

      "rows": 1000,

      "filtered": 100,

      "index_condition": "t1.start_date >= '2019-02-10' and t1.end_date < '2019-04-01'"

    }

  }

}

    "range_scan_alternatives": [

      {

        "index": "start_date",

        "ranges": ["0x4ac60f <= start_date"],

        "rowid_ordered": false,

        "using_mrr": false,

        "index_only": false,

        "rows": 1000,

        "cost": 1252.4,

        "chosen": true

      }

    ],