mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| test               |
+--------------------+
3 rows in set (0.00 sec)

mysql> create database a;
Query OK, 1 row affected (0.00 sec)

mysql> create database aaa;
Query OK, 1 row affected (0.00 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| a                  |
| aaa                |
| mysql              |
| test               |
+--------------------+
5 rows in set (0.00 sec)

mysql> use a;
ERROR 1049 (42000): Unknown database 'a;'
mysql> use a
Database changed
mysql> use aaa;
ERROR 1049 (42000): Unknown database 'aaa;'
mysql> use aaa
Database changed
mysql> select database();
+------------+
| database() |
+------------+
| aaa        |
+------------+
1 row in set (0.01 sec)

mysql> use test;
Database changed