MariaDB [test]> create table t1 (i int) charset latin1;

Query OK, 0 rows affected (0.43 sec)

MariaDB [test]> alter table t1 convert to character set utf8;

Query OK, 0 rows affected (0.00 sec)

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> show create table t1 \G

*************************** 1. row ***************************

       Table: t1

Create Table: CREATE TABLE `t1` (

  `i` int(11) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=latin1

1 row in set (0.00 sec)

MariaDB [test]> alter table t1 convert to character set utf8, force;

Query OK, 0 rows affected (1.16 sec)

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> show create table t1 \G

*************************** 1. row ***************************

       Table: t1

Create Table: CREATE TABLE `t1` (

  `i` int(11) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8

1 row in set (0.00 sec)

MariaDB [test]> alter table t1 convert to character set utf8, algorithm=copy;

Query OK, 0 rows affected (1.16 sec)

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> show create table t1 \G

*************************** 1. row ***************************

       Table: t1

Create Table: CREATE TABLE `t1` (

  `i` int(11) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8

1 row in set (0.00 sec)

MariaDB [test]> create table t1 (c char) charset latin1;

Query OK, 0 rows affected (0.33 sec)

MariaDB [test]> alter table t1 convert to character set utf8;

Query OK, 0 rows affected (1.18 sec)               

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> show create table t1 \G

*************************** 1. row ***************************

       Table: t1

Create Table: CREATE TABLE `t1` (

  `c` char(1) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8

1 row in set (0.00 sec)