MariaDB / MySQL - username length

MariaDB 10.1.13

[root@gabriel-laptop batch]# docker run --name some-mariadb -e MYSQL_ROOT_PASSWORD=test -d mariadb:latest
6c413f68aa72c13a56f6d10c677cd547a2d607b7309ef85679718208350f5710
[root@gabriel-laptop batch]# docker exec -it some-mariadb bash
root@6c413f68aa72:/# export TERM=dumb
root@6c413f68aa72:/# mysql -uroot -ptest
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 10.1.13-MariaDB-1~jessie mariadb.org binary distribution

Copyright (c) 2000, 2016, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> GRANT ALL PRIVILEGES ON *.* TO 'u01234567890123456789'@'%' IDENTIFIED BY PASSWORD '*8A3...lalala...' WITH GRANT OPTION;
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> Bye
root@6c413f68aa72:/# mysql -uu01234567890123456789 -p
Enter password: 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 3
Server version: 10.1.13-MariaDB-1~jessie mariadb.org binary distribution

Copyright (c) 2000, 2016, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> select user();
+---------------------------------+
| user()                          |
+---------------------------------+
| u01234567890123456789@localhost |
+---------------------------------+
1 row in set (0.00 sec)

MariaDB [(none)]> SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA='mysql' AND TABLE_NAME='user' AND COLUMN_NAME = 'user' \G
*************************** 1. row ***************************
           TABLE_CATALOG: def
            TABLE_SCHEMA: mysql
              TABLE_NAME: user
             COLUMN_NAME: User
        ORDINAL_POSITION: 2
          COLUMN_DEFAULT: 
             IS_NULLABLE: NO
               DATA_TYPE: char
CHARACTER_MAXIMUM_LENGTH: 80
  CHARACTER_OCTET_LENGTH: 240
       NUMERIC_PRECISION: NULL
           NUMERIC_SCALE: NULL
      DATETIME_PRECISION: NULL
      CHARACTER_SET_NAME: utf8
          COLLATION_NAME: utf8_bin
             COLUMN_TYPE: char(80)
              COLUMN_KEY: PRI
                   EXTRA: 
              PRIVILEGES: select,insert,update,references
          COLUMN_COMMENT: 
1 row in set (0.00 sec)

MySQL 5.7.12

[root@gabriel-laptop batch]# docker run --name some-mysql -e MYSQL_ROOT_PASSWORD=test -d mysql:latest
4e033c5354d318518bced38c35ec440735558feee5e321041eea4b5360ed1111
Usage of loopback devices is strongly discouraged for production use. Either use `--storage-opt dm.thinpooldev` or use `--storage-opt dm.no_warn_on_loop_devices=true` to suppress this warning.
[root@gabriel-laptop batch]# docker exec -it some-mysql bash
root@4e033c5354d3:/# mysql -uroot -ptest
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.12 MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> GRANT ALL PRIVILEGES ON *.* TO 'u01234567890123456789'@'%' IDENTIFIED BY PASSWORD '*8A3...lalala...' WITH GRANT OPTION;
Query OK, 0 rows affected, 2 warnings (0.00 sec)

mysql> SHOW WARNINGS;
+---------+------+---------------------------------------------------------------------------------------------------------------------------------------+
| Level   | Code | Message                                                                                                                               |
+---------+------+---------------------------------------------------------------------------------------------------------------------------------------+
| Warning | 1287 | 'IDENTIFIED BY PASSWORD' is deprecated and will be removed in a future release. Please use IDENTIFIED WITH <plugin> AS <hash> instead |
| Warning | 1287 | Using GRANT for creating new user is deprecated and will be removed in future release. Create new user with CREATE USER statement.    |
+---------+------+---------------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

mysql> ^DBye
root@4e033c5354d3:/# mysql -uu01234567890123456789 -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.12 MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> select user();
+---------------------------------+
| user()                          |
+---------------------------------+
| u01234567890123456789@localhost |
+---------------------------------+
1 row in set (0.00 sec)

mysql> SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA='mysql' AND TABLE_NAME='user' AND COLUMN_NAME = 'user' \G
*************************** 1. row ***************************
           TABLE_CATALOG: def
            TABLE_SCHEMA: mysql
              TABLE_NAME: user
             COLUMN_NAME: User
        ORDINAL_POSITION: 2
          COLUMN_DEFAULT: 
             IS_NULLABLE: NO
               DATA_TYPE: char
CHARACTER_MAXIMUM_LENGTH: 32
  CHARACTER_OCTET_LENGTH: 96
       NUMERIC_PRECISION: NULL
           NUMERIC_SCALE: NULL
      DATETIME_PRECISION: NULL
      CHARACTER_SET_NAME: utf8
          COLLATION_NAME: utf8_bin
             COLUMN_TYPE: char(32)
              COLUMN_KEY: PRI
                   EXTRA: 
              PRIVILEGES: select,insert,update,references
          COLUMN_COMMENT: 
   GENERATION_EXPRESSION: 
1 row in set (0.00 sec)