显示所有的数据库

shwo databases;

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.02 sec)

了解如下四个数据库的作用

1. information_schema
2. mysql
3. performance_schema
4. sys