怎么修改MySQL root用户口令

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1.一些基本概念

1)MySQL体系结构由五个主子系统组成：查询引擎、存储管理器、缓冲管理器、事务管理器和恢复管理器。
2)查询引擎包含三个相关联的部件：语法分析器、查询优化器和执行部件。
3)除五个主子系统以外，MySQL体系结构还包括两个辅助部件：过程管理器和函数库。
4)在MySQL中，事务的开始标记为一个BEGIN语句（与Oracle不同）。

2.安装完成后修改MySQL root用户口令

C:Documents and SettingsAdministrator>mysql -u root
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 18
Server version: 5.1.34-community MySQL Community Server (GPL)

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

mysql> use mysql
Database changed
mysql> set password for 'root'@'localhost' = password('passwd');
Query OK, 0 rows affected (0.00 sec)

mysql> quit
Bye

[@more@]C:Documents and SettingsAdministrator>mysql -u root
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: N
O)

C:Documents and SettingsAdministrator>mysql -u root -p
Enter password: ******
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 20
Server version: 5.1.34-community MySQL Community Server (GPL)

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

3.修改数据文件存放路径

先关闭MySQL服务器：

C:Documents and SettingsAdministrator>mysqladmin -u root -p shutdown
Enter password: ******

修改my.ini配置文件（默认放在 D:Program FilesMySQLMySQL Server 5.1 下）中的datadir参数：

#Path to the database root
datadir="D:MySQL Datafilesdata"

启动MySQL服务器，可以通过启动系统服务的方法。

4.一系列简单操作

1)创建数据库，查看数据库，选择想要使用的数据库

mysql> create database ggyy;
Query OK, 1 row affected (0.43 sec)

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

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

mysql> use ggyy
Database changed

2)创建表，查看表

mysql> create table members
-> (
-> id int(3) auto_increment,
-> fname varchar(20) not null,
-> lname varchar(20) not null,
-> tel varchar(15),
-> email varchar(50),
-> primary key (id)
-> );
Query OK, 0 rows affected (0.49 sec)

mysql> show tables;
+----------------+
| Tables_in_ggyy |
+----------------+
| members |
+----------------+
1 row in set (0.01 sec)

注：auto_increment修饰符只适用于整型字段，表明MySQL将要为这个字段自动生成一个数字（通过对前面的值增加1）。一个表只能有一个auto_increment字段，而且这个字段必须被定义为键（即字段上必须有索引，术语"键"和"索引"在MySQL中是等同的）。

这时可以在数据文件的存放路径下看到新生成的文件：

D:MySQL Datafilesdataggyy>dir
Volume in drive D is Data
Volume Serial Number is D632-9209

Directory of D:MySQL Datafilesdataggyy

2009-05-18 10:58

.
2009-05-18 10:58
..
2009-05-18 10:18 65 db.opt
2009-05-18 10:36 8,680 members.frm
2 File(s) 8,745 bytes
2 Dir(s) 66,038,996,992 bytes free

3)添加列，修改列，删除列

mysql> desc members;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int(3) | NO | PRI | NULL | auto_increment |
| fname | varchar(20) | NO | | NULL | |
| lname | varchar(20) | NO | | NULL | |
| tel | varchar(15) | YES | | NULL | |
| email | varchar(50) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
5 rows in set (0.01 sec)

mysql> alter table members add remark varchar(50);
Query OK, 0 rows affected (0.67 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc members;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(3) | NO | PRI | NULL | auto_increment |
| fname | varchar(20) | NO | | NULL | |
| lname | varchar(20) | NO | | NULL | |
| tel | varchar(15) | YES | | NULL | |
| email | varchar(50) | YES | | NULL | |
| remark | varchar(50) | YES | | NULL | |
+--------+-------------+------+-----+---------+----------------+
6 rows in set (0.04 sec)

mysql> alter table members modify remark varchar(100);
Query OK, 0 rows affected (0.18 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc members;
+--------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+--------------+------+-----+---------+----------------+
| id | int(3) | NO | PRI | NULL | auto_increment |
| fname | varchar(20) | NO | | NULL | |
| lname | varchar(20) | NO | | NULL | |
| tel | varchar(15) | YES | | NULL | |
| email | varchar(50) | YES | | NULL | |
| remark | varchar(100) | YES | | NULL | |
+--------+--------------+------+-----+---------+----------------+
6 rows in set (0.01 sec)

mysql> alter table members drop remark;
Query OK, 0 rows affected (0.18 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> desc members;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int(3) | NO | PRI | NULL | auto_increment |
| fname | varchar(20) | NO | | NULL | |
| lname | varchar(20) | NO | | NULL | |
| tel | varchar(15) | YES | | NULL | |
| email | varchar(50) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
5 rows in set (0.01 sec)

4)插入记录，查询表，修改记录，删除记录

mysql> insert into members (id, fname, lname, tel, email) values (1, 'Yue', 'Gao
', '1234567', 'yuegao@company.com');
Query OK, 1 row affected (0.07 sec)

mysql> insert into members values (3, 'Feng', 'Song', '7654321', 'fengsong@compa
ny.com');
Query OK, 1 row affected (0.43 sec)

mysql> select * from members;
+----+-------+-------+---------+----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+----------------------+
| 1 | Yue | Gao | 1234567 | yuegao@company.com |
| 3 | Feng | Song | 7654321 | fengsong@company.com |
+----+-------+-------+---------+----------------------+
2 rows in set (0.00 sec)

mysql> select * from members;
+----+-------+-------+---------+----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+----------------------+
| 1 | Yue | Gao | 1234567 | yuegao@company.com |
| 3 | Feng | Song | 7654321 | fengsong@company.com |
+----+-------+-------+---------+----------------------+
2 rows in set (0.01 sec)

mysql> insert into members (fname, lname, email) values ('Chen', 'Chu', 'chenchu
@company.com');
Query OK, 1 row affected (0.44 sec)

mysql> select * from members;
+----+-------+-------+---------+----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+----------------------+
| 1 | Yue | Gao | 1234567 | yuegao@company.com |
| 3 | Feng | Song | 7654321 | fengsong@company.com |
| 4 | Chen | Chu | NULL | chenchu@company.com |
+----+-------+-------+---------+----------------------+
3 rows in set (0.00 sec)

这里可以看到auto_increment修饰符的作用，自动将新插入的记录id段的值设置为4，而不是2。

mysql> update members set id = 2 where id = 3;
Query OK, 1 row affected (0.05 sec)
Rows matched: 1 Changed: 1 Warnings: 0

mysql> select * from members;
+----+-------+-------+---------+----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+----------------------+
| 1 | Yue | Gao | 1234567 | yuegao@company.com |
| 2 | Feng | Song | 7654321 | fengsong@company.com |
| 4 | Chen | Chu | NULL | chenchu@company.com |
+----+-------+-------+---------+----------------------+
3 rows in set (0.00 sec)

mysql> delete from members where id = 4;
Query OK, 1 row affected (0.43 sec)

mysql> select * from members;
+----+-------+-------+---------+----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+----------------------+
| 1 | Yue | Gao | 1234567 | yuegao@company.com |
| 2 | Feng | Song | 7654321 | fengsong@company.com |
+----+-------+-------+---------+----------------------+
2 rows in set (0.00 sec)

mysql> insert into members (fname, lname, email) values ('Chen', 'Chu', 'chenchu
@company.com');
Query OK, 1 row affected (0.43 sec)

mysql> select * from members;
+----+-------+-------+---------+----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+----------------------+
| 1 | Yue | Gao | 1234567 | yuegao@company.com |
| 2 | Feng | Song | 7654321 | fengsong@company.com |
| 5 | Chen | Chu | NULL | chenchu@company.com |
+----+-------+-------+---------+----------------------+
3 rows in set (0.00 sec)

注：这里可以看到新插入的记录id字段的值为5，即使表中已不存在id为3或4的记录。也就是说，auto_increment修饰符不会重用那些曾经使用过的值。

5)limit关键字

使用limit关键字可以对结果集进行限制，它有两个参数，用逗号隔开，分别指定从哪行开始显示和显示多少行。如果只跟一个参数，则指定从结果集合的开头返回的行数。

mysql> select * from members limit 3,3;
Empty set (0.00 sec)

mysql> select * from members limit 2,3;
+----+-------+-------+------+---------------------+
| id | fname | lname | tel | email |
+----+-------+-------+------+---------------------+
| 5 | Chen | Chu | NULL | chenchu@company.com |
+----+-------+-------+------+---------------------+
1 row in set (0.01 sec)

mysql> select * from members limit 1, 3;
+----+-------+-------+---------+----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+----------------------+
| 2 | Feng | Song | 7654321 | fengsong@company.com |
| 5 | Chen | Chu | NULL | chenchu@company.com |
+----+-------+-------+---------+----------------------+
2 rows in set (0.00 sec)

mysql> select * from members limit 0, 3;
+----+-------+-------+---------+----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+----------------------+
| 1 | Yue | Gao | 1234567 | yuegao@company.com |
| 2 | Feng | Song | 7654321 | fengsong@company.com |
| 5 | Chen | Chu | NULL | chenchu@company.com |
+----+-------+-------+---------+----------------------+
3 rows in set (0.00 sec)

可以看到行号是从0开始的，并且3条记录的行号是连续的。id为2的记录是删除后重新插入的，重新插入时id为5的记录已经存在，但id为2的记录还是排在了前面。

mysql> insert into members values (6, 'Chao', 'Zhang', '6666666', 'chaozhang@com
pany.com');

mysql> select * from members limit 3,4;
+----+-------+-------+---------+-----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+-----------------------+
| 6 | Chao | Zhang | 6666666 | chaozhang@company.com |
+----+-------+-------+---------+-----------------------+
1 row in set (0.00 sec)

mysql> select * from members limit 2,4;
+----+-------+-------+---------+-----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+-----------------------+
| 5 | Chen | Chu | NULL | chenchu@company.com |
| 6 | Chao | Zhang | 6666666 | chaozhang@company.com |
+----+-------+-------+---------+-----------------------+
2 rows in set (0.00 sec)

插入一条id为6的记录，它排在了id为5的记录之后。再插入两条记录进行观察：

mysql> insert into members values (8, 'Chen', 'Zhang', '8888888', 'chenzhang@com
pany.com');
Query OK, 1 row affected (0.43 sec)

mysql> insert into members values (7, 'Yifei', 'Yin', '7777777', 'yfyin@company.
com');
Query OK, 1 row affected (0.42 sec)

mysql> select * from members limit 5,6;
+----+-------+-------+---------+-----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+-----------------------+
| 8 | Chen | Zhang | 8888888 | chenzhang@company.com |
+----+-------+-------+---------+-----------------------+
1 row in set (0.00 sec)

mysql> select * from members limit 4,6;
+----+-------+-------+---------+-----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+-----------------------+
| 7 | Yifei | Yin | 7777777 | yfyin@company.com |
| 8 | Chen | Zhang | 8888888 | chenzhang@company.com |
+----+-------+-------+---------+-----------------------+
2 rows in set (0.01 sec)

mysql> select * from members limit 3,6;
+----+-------+-------+---------+-----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+-----------------------+
| 6 | Chao | Zhang | 6666666 | chaozhang@company.com |
| 7 | Yifei | Yin | 7777777 | yfyin@company.com |
| 8 | Chen | Zhang | 8888888 | chenzhang@company.com |
+----+-------+-------+---------+-----------------------+
3 rows in set (0.00 sec)

可以看到，不管是重新插入删除掉的记录的也好，让id值较大的记录比id值较小的记录先插入也好，行号的大小顺序好像都是由id字段的大小顺序决定的。而"select * from members;"的结果则体现了行号的大小顺序。

mysql> select * from members;
+----+-------+-------+---------+-----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+-----------------------+
| 1 | Yue | Gao | 1234567 | yuegao@company.com |
| 2 | Feng | Song | 7654321 | fengsong@company.com |
| 5 | Chen | Chu | NULL | chenchu@company.com |
| 6 | Chao | Zhang | 6666666 | chaozhang@company.com |
| 7 | Yifei | Yin | 7777777 | yfyin@company.com |
| 8 | Chen | Zhang | 8888888 | chenzhang@company.com |
+----+-------+-------+---------+-----------------------+
6 rows in set (0.00 sec)

为了确定这种猜测，再做一组实验：

mysql> create table members_temp
-> (
-> id int(3),
-> fname varchar(20),
-> lname varchar(20),
-> tel varchar(15),
-> email varchar(50)
-> );
Query OK, 0 rows affected (0.48 sec)

mysql> insert into members_temp (id, fname, lname) values (1, 'Yue', 'Gao');
Query OK, 1 row affected (0.43 sec)

mysql> insert into members_temp (id, fname, lname) values (2, 'Feng', 'Song');
Query OK, 1 row affected (0.03 sec)

mysql> insert into members_temp (id, fname, lname) values (5, 'Chen', 'Chu');
Query OK, 1 row affected (0.43 sec)

mysql> select * from members_temp;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 2 | Feng | Song | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
+------+-------+-------+------+-------+
3 rows in set (0.00 sec)

mysql> select * from members_temp limit 2,3;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 5 | Chen | Chu | NULL | NULL |
+------+-------+-------+------+-------+
1 row in set (0.01 sec)

mysql> select * from members_temp limit 1,3;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 2 | Feng | Song | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
+------+-------+-------+------+-------+
2 rows in set (0.00 sec)

mysql> select * from members_temp limit 0,3;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 2 | Feng | Song | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
+------+-------+-------+------+-------+
3 rows in set (0.00 sec)

mysql> insert into members_temp (id, fname, lname) values (3, 'Yifei', 'Yin');
Query OK, 1 row affected (0.42 sec)

mysql> select * from members_temp;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 2 | Feng | Song | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
+------+-------+-------+------+-------+
4 rows in set (0.00 sec)

mysql> select * from members_temp limit 3,4;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 3 | Yifei | Yin | NULL | NULL |
+------+-------+-------+------+-------+
1 row in set (0.00 sec)

mysql> select * from members_temp limit 2,4;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 5 | Chen | Chu | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
+------+-------+-------+------+-------+
2 rows in set (0.00 sec)

mysql> delete from members_temp where id = 2;
Query OK, 1 row affected (0.42 sec)

mysql> select * from members_temp;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
+------+-------+-------+------+-------+
3 rows in set (0.00 sec)

mysql> insert into members_temp (id, fname, lname) values (2, 'Feng', 'Song');
Query OK, 1 row affected (0.03 sec)

mysql> select * from members_temp;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
| 2 | Feng | Song | NULL | NULL |
+------+-------+-------+------+-------+
4 rows in set (0.00 sec)

到这里可以看到，新创建的表没有索引，也没有主键，不管是让id值较大的记录比id值较小的记录先插入也好，重新插入删除掉的记录的也好，行号都是由记录插入的先后顺序决定的。

mysql> create index id_idx on members_temp (id);
Query OK, 4 rows affected (0.71 sec)
Records: 4 Duplicates: 0 Warnings: 0

mysql> select * from members_temp;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
| 2 | Feng | Song | NULL | NULL |
+------+-------+-------+------+-------+
4 rows in set (0.00 sec)

mysql> delete from members_temp where id = 5;
Query OK, 1 row affected (0.03 sec)

mysql> insert into members_temp (id, fname, lname) values (5, 'Chen', 'Chu');
Query OK, 1 row affected (0.04 sec)

mysql> select * from members_temp;
+------+-------+-------+------+-------+
| id | fname | lname | tel | email |
+------+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
| 2 | Feng | Song | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
+------+-------+-------+------+-------+
4 rows in set (0.00 sec)

在id列上创建索引，依然如此。

mysql> alter table members_temp add constraint primary key (id);
Query OK, 4 rows affected (0.64 sec)
Records: 4 Duplicates: 0 Warnings: 0

mysql> select * from members_temp;
+----+-------+-------+------+-------+
| id | fname | lname | tel | email |
+----+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 2 | Feng | Song | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
+----+-------+-------+------+-------+
4 rows in set (0.01 sec)

mysql> delete from members_temp where id = 2;
Query OK, 1 row affected (0.45 sec)

mysql> insert into members_temp (id, fname, lname) values (2, 'Feng', 'Song');
Query OK, 1 row affected (0.03 sec)

mysql> select * from members_temp;
+----+-------+-------+------+-------+
| id | fname | lname | tel | email |
+----+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 2 | Feng | Song | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
+----+-------+-------+------+-------+
4 rows in set (0.00 sec)

mysql> select * from members_temp limit 3,4;
+----+-------+-------+------+-------+
| id | fname | lname | tel | email |
+----+-------+-------+------+-------+
| 5 | Chen | Chu | NULL | NULL |
+----+-------+-------+------+-------+
1 row in set (0.00 sec)

mysql> select * from members_temp limit 2,4;
+----+-------+-------+------+-------+
| id | fname | lname | tel | email |
+----+-------+-------+------+-------+
| 3 | Yifei | Yin | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
+----+-------+-------+------+-------+
2 rows in set (0.00 sec)

mysql> select * from members_temp limit 1,4;
+----+-------+-------+------+-------+
| id | fname | lname | tel | email |
+----+-------+-------+------+-------+
| 2 | Feng | Song | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
+----+-------+-------+------+-------+
3 rows in set (0.00 sec)

mysql> select * from members_temp limit 0,4;
+----+-------+-------+------+-------+
| id | fname | lname | tel | email |
+----+-------+-------+------+-------+
| 1 | Yue | Gao | NULL | NULL |
| 2 | Feng | Song | NULL | NULL |
| 3 | Yifei | Yin | NULL | NULL |
| 5 | Chen | Chu | NULL | NULL |
+----+-------+-------+------+-------+
4 rows in set (0.00 sec)

mysql> select * from members;
+----+-------+-------+---------+-----------------------+
| id | fname | lname | tel | email |
+----+-------+-------+---------+-----------------------+
| 1 | Yue | Gao | 1234567 | yuegao@company.com |
| 2 | Feng | Song | 7654321 | fengsong@company.com |
| 5 | Chen | Chu | NULL | chenchu@company.com |
| 6 | Chao | Zhang | 6666666 | chaozhang@company.com |
| 7 | Yifei | Yin | 7777777 | yfyin@company.com |
| 8 | Chen | Zhang | 8888888 | chenzhang@company.com |
+----+-------+-------+---------+-----------------------+
6 rows in set (0.00 sec)

在id列上添加主键后，行号变为由id列的大小顺序决定，这就证明了之前的猜想。

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