Index usage for DATE(datetime_column) = const does not work for engine Memory

"access_type": "range"

"index_condition": "t1.a between '2009-01-01 00:00:00' and '2009-12-31 23:59:59'"

"access_type": "ALL"

"attached_condition": "year(t1.a) = 2009"

create table t1 (pk int primary key, a datetime, key(a)) engine=memory;

INSERT INTO t1 (pk,a) VALUES (1,'2009-11-29 13:43:32');

INSERT INTO t1 (pk,a) VALUES (2,'2009-11-29 03:23:32');

INSERT INTO t1 (pk,a) VALUES (3,'2009-10-16 05:56:32');

INSERT INTO t1 (pk,a) VALUES (4,'2010-11-29 13:43:32');

INSERT INTO t1 (pk,a) VALUES (5,'2010-10-16 05:56:32');

INSERT INTO t1 (pk,a) VALUES (6,'2011-11-29 13:43:32');

INSERT INTO t1 (pk,a) VALUES (7,'2012-10-16 05:56:32');

explain format=json  select * from t1 where year(a) = 2009;

drop table t1;

explain format=json  select * from t1 where year(a) = 2009;

EXPLAIN

{

  "query_block": {

    "select_id": 1,

    "cost": 0.010296454,

    "nested_loop": [

      {

        "table": {

          "table_name": "t1",

          "access_type": "ALL",

          "loops": 1,

          "rows": 7,

          "cost": 0.010296454,

          "filtered": 100,

          "attached_condition": "year(t1.a) = 2009"

        }

      }

    ]

  }

}