Rounding functions return wrong data types for DATE input

CREATE OR REPLACE TABLE t1 (a date);

CREATE OR REPLACE TABLE t2 AS SELECT FLOOR(a), CEIL(a),ROUND(a),TRUNCATE(a,0) FROM t1;

+---------------+--------------+------+-----+---------+-------+

| Field         | Type         | Null | Key | Default | Extra |

+---------------+--------------+------+-----+---------+-------+

| FLOOR(a)      | bigint(12)   | YES  |     | NULL    |       |

| CEIL(a)       | bigint(12)   | YES  |     | NULL    |       |

| ROUND(a)      | double(17,0) | YES  |     | NULL    |       |

| TRUNCATE(a,0) | double(17,0) | YES  |     | NULL    |       |

+---------------+--------------+------+-----+---------+-------+