UNION is not symmetric when mixing INT and CHAR

CREATE OR REPLACE TABLE t1 AS SELECT 1, 'a' AS c1 UNION SELECT 'a', 1;

SHOW CREATE TABLE t1;

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

| Table | Create Table                                                                                                                                                                  |

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

| t1    | CREATE TABLE `t1` (

  `1` varchar(1) CHARACTER SET utf8 NOT NULL DEFAULT '',

  `c1` varchar(20) CHARACTER SET utf8 NOT NULL DEFAULT ''

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

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

CREATE OR REPLACE TABLE t1 AS SELECT COALESCE(1,'a'), COALESCE('a',1);

SHOW CREATE TABLE t1;

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

| Table | Create Table                                                                                                                                                                                            |

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

| t1    | CREATE TABLE `t1` (

  `COALESCE(1,'a')` varchar(1) CHARACTER SET utf8 NOT NULL DEFAULT '',

  `COALESCE('a',1)` varchar(1) CHARACTER SET utf8 NOT NULL DEFAULT ''

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

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