select rtrim command result is truncated

MariaDB [mydb]> show create table t2;

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

| Table | Create Table                                                                           |

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

| t2    | CREATE TABLE `t2` (

  `col` double DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

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

1 row in set (0.000 sec)

MariaDB [mydb]> select col from t2;

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

| col                     |

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

| -1.7976931348623157e308 |

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

1 row in set (0.000 sec)

MariaDB [mydb]> select rtrim(col) from t2;

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

| rtrim(col)              |

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

| -1.7976931348623157e308 |

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

1 row in set (0.000 sec)

MariaDB [mydb]> select col from t2 group by 1;

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

| col                     |

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

| -1.7976931348623157e308 |

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

1 row in set (0.001 sec)

MariaDB [mydb]> select rtrim(col) from t2 group by 1;

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

| rtrim(col)             |

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

| -1.7976931348623157e30 |

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

1 row in set (0.001 sec)