MariaDB [test]> create table t1(f float);

Query OK, 0 rows affected (0.03 sec)

MariaDB [test]> insert into t1 values(1.1);

Query OK, 1 row affected (0.02 sec)

MariaDB [test]> select f from t1 union select 1;

+------+

| f    |

+------+

|  1.1 |

|    1 |

+------+

2 rows in set (0.00 sec)

MariaDB [test]> select 1 union select f from t1;

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

| 1                 |

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

|                 1 |

| 1.100000023841858 |

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

2 rows in set (0.00 sec)

MariaDB [test]> select "foo" union select f from t1;

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

| foo          |

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

| foo          |

| 1.1000000238 |

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

2 rows in set (0.00 sec)