DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a TIMESTAMP);

DROP TABLE IF EXISTS t2;

CREATE TABLE t2 AS SELECT

  MAX(a),

  COALESCE(a),

  COALESCE(MAX(a)),

  MAX(COALESCE(a))

FROM t1;

SHOW CREATE TABLE t2;

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

| Table | Create Table                                                                                                                                                                                                                                 |

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

| t2    | CREATE TABLE `t2` (

  `MAX(a)` timestamp NULL DEFAULT NULL,

  `COALESCE(a)` timestamp NULL DEFAULT NULL,

  `COALESCE(MAX(a))` timestamp NULL DEFAULT NULL,

  `MAX(COALESCE(a))` datetime DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

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

mysql --column-type-info test

SELECT

  MAX(a),

  COALESCE(a),

  COALESCE(MAX(a)),

  MAX(COALESCE(a))

FROM t1;

Field   1:  `MAX(a)`

Type:       TIMESTAMP

...

Field   2:  `COALESCE(a)`

Type:       TIMESTAMP

...

Field   3:  `COALESCE(MAX(a))`

Type:       TIMESTAMP

...

Field   4:  `MAX(COALESCE(a))`

Type:       TIMESTAMP

Collation:  binary (63)