MySQL的管理员用户名为root，密码默认为空。
1、修改 root密码
   MYSQL配置好后，启动成功，默认密码是空，但是为了安全，设置密码（mysql有
   一个默认的用户名为root，密码自己定。）
   cmd
   然后输入 mysql -uroot -pa123;按enter键
   出现 Enter password: 这个，还是按enter键，这样成功进入
   修改密码：update mysql.user set password=password('a123') where 
   user='root';
   执行：flush privileges;
   解释：flush privileges 命令本质上的作用是将
   当前user和priviligeS表中的用户信息/权限设置从mysql库(MySQL数据库的内置
   库
   )
   中提取到内存里。MySQL用户数据和权限有修改后，
   希望在"不重启MySQL服务"的情况下直接生效，
   那么就需要执行这个命令。通常是在修改ROOT帐号的设置后，
   怕重启后无法再登录进来，那么直接flush之后就可以看权限设置是否生效。
   而不必冒太大风险。
2、步骤如下：
   
C:\Users\Administrator>mysql -uroot -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 14
Server version: 5.1.73-community MySQL Community Server (GPL)

Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights rese

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 sta

mysql> update mysql.user set password=password('root') where user='root';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 0  Changed: 0  Warnings: 0

mysql> flush privileges;
Query OK, 0 rows affected (0.01 sec)

mysql>

下面一段也可以：

C:\Users\Administrator>mysql -u root
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 14
Server version: 5.1.73-community MySQL Community Server (GPL)

Copyright (c) 2000, 2013, 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> use mysql
Database changed
mysql> update user set password=old_password('a123') where user='root' and 
host=
'localhost'
    -> ;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> flush privileges;
Query OK, 0 rows affected (0.08 sec)

2.查看环境变量 的值

C:\Users\Administrator>set path
Path=D:\software\oracle\product\10.2.0\db_1\bin;D:\software\Java\jdk1.7.0_
40\bin
;D:\software\Java\jdk1.7.0_40\jre\bin;D:\software\MySQL Server 5.1\bin\;
PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC

C:\Users\Administrator>
3.cmd环境下，进入到mysql中，如何退出

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

mysql> exit
Bye

C:\Users\Administrator>mysql -uroot -pa123
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 26
Server version: 5.1.73-community MySQL Community Server (GPL)

Copyright (c) 2000, 2013, 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> \q;
Bye

C:\Users\Administrator>

4.模糊查询：模糊查询为test的数据库
    show databases LIKE '%test%';

5.展示有哪些表：mysql>show tables;

6.mysql>use information_schema;
  mysql>select * from tables;//查询该数据库下的所有表

7.查看表的结构
  mysql>desc dept;//查看部门表的结构

8.主键约束与唯一约束的区别
   主键约束不能为空，且不能重复；(PRIMARY)
   唯一约束可以为空，但是不能重复；（UNIQUE）
9.查看创建表的语句
   mysql>show create table emp ;
10. now()代表当前时间；

11.select length(sname),length(id) from test_char;