MySQL第二课（库的操作、表的操作、数据类型）

库操作&表操作：

mysql> create database a; //创建数据库a

Query OK, 1 row affected (0.00 sec)

mysql> show create database a;

+----------+--------------------------------------------------------------+

| Database | Create Database |

+----------+--------------------------------------------------------------+

| a | CREATE DATABASE `a` /*!40100 DEFAULT CHARACTER SET latin1 */ | //latin1是当前使用的字符编码格式

+----------+--------------------------------------------------------------+

1 row in set (0.00 sec

mysql> show charset; //显示字符编码

……

mysql> help create database; //获取create database的帮助

……

mysql> create database b default charset=utf8; //创建数据库b，并指定（更改）默认字符编码为utf8

mysql> show create database b; //显示创建数据库b的信息

+----------+------------------------------------------------------------+

| Database | Create Database |

+----------+------------------------------------------------------------+

| b | CREATE DATABASE `b` /*!40100 DEFAULT CHARACTER SET utf8 */ |

+----------+------------------------------------------------------------+

mysql> create table if not exists student (name varchar(32)); //创建student表

Query OK, 0 rows affected (0.03 sec)

mysql> insert into student values ('a'),('A'),('b'),('B'); //写入四条数据

Query OK, 4 rows affected (0.00 sec)

Records: 4 Duplicates: 0 Warnings: 0

mysql> select * from student; //显示表中数据

+------+

| name |

+------+

| a |

| A |

| b |

| B |

+------+

4 rows in set (0.00 sec)

mysql> select * from student where name ='a'; //默认的校验规则不分大小写，所以a和A都显示

+------+

| name |

+------+

| a |

| A |

+------+

2 rows in set (0.00 sec)

show collation; //显示校验规则

mysql> create database if not exists c default charset=utf8 collate utf8_bin;

//创建数据库c，默认编码为utf8，默认校验规则为 collate utf8_bin

Query OK, 1 row affected (0.00 sec)

mysql> show create database c; //显示？……

+----------+-----------------------------------------------------------------------------+

| Database | Create Database |

+----------+-----------------------------------------------------------------------------+

| c | CREATE DATABASE `c` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_bin */ |

+----------+-----------------------------------------------------------------------------+

1 row in set (0.00 sec)

mysql> use c;

Database changed

mysql> create table if not exists student (name varchar(32)); //创建student表

Query OK, 0 rows affected (0.01 sec)

mysql> insert into student values ('a'),('A'),('b'),('B'); //写入数据

Query OK, 4 rows affected (0.00 sec)

Records: 4 Duplicates: 0 Warnings: 0

mysql> select * from student where name='a'; //utf8_bin区分大小写，所以只有a

+------+

| name |

+------+

| a |

+------+

1 row in set (0.00 sec)

mysql> select * from student order by name; //依据名字排序校验规则也会影响排序

+------+

| name |

+------+

| A |

| B |

| a |

| b |

+------+

4 rows in set (0.00 sec)

校验规则的影响：

（1）大小写（不区分大小写：邮箱、windows创建文件夹的名字；区分大小写：密码、linux系统下的文件名）

（2）排序

mysql> exit //退出数据库

Bye

[du@localhost ~]$ which mysql //查看mysql所在位置

/usr/bin/mysql

[du@localhost ~]$ ls /usr/bin/mysql*

/usr/bin/mysql /usr/bin/mysql_fix_privilege_tables

/usr/bin/mysqlaccess /usr/bin/mysqlhotcopy

/usr/bin/mysqladmin /usr/bin/mysqlimport

/usr/bin/mysqlbinlog /usr/bin/mysql_install_db

/usr/bin/mysqlbug /usr/bin/mysql_secure_installation

/usr/bin/mysqlcheck /usr/bin/mysql_setpermission

/usr/bin/mysql_config /usr/bin/mysqlshow

/usr/bin/mysql_convert_table_format /usr/bin/mysqlslap

/usr/bin/mysqld_multi /usr/bin/mysqltest

/usr/bin/mysqld_safe /usr/bin/mysql_tzinfo_to_sql

/usr/bin/mysqldump /usr/bin/mysql_upgrade

/usr/bin/mysqldumpslow /usr/bin/mysql_waitpid

/usr/bin/mysql_find_rows /usr/bin/mysql_zap

/usr/bin/mysql_fix_extensions

[du@localhost ~]$ mysqldump //备份命令

Usage: mysqldump [OPTIONS] database [tables]

OR mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...]

OR mysqldump [OPTIONS] --all-databases [OPTIONS]

For more options, use mysqldump --help

[du@localhost ~]$ mysqldump -u root -p --databases c > /c_db.sql //备份数据库c （重定义>为/c_db.sql)

bash: /c_db.sql: Permission denied //转到root用户下再执行

[du@localhost ~]$ su - root

[root@localhost ~]# mysqldump -u root -p --databases b > /c_db.sql //备份数据库c到/c_db.sql

Enter password:

[root@localhost ~]# mysql -u root -p //再次连接数据库

Enter password:

Welcome to the MySQL monitor. Commands end with ; or \g.

Your MySQL connection id is 11

Server version: 5.1.73 Source distribution

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> drop database b; //前面已经备份成功，这里可以删除数据库b

Query OK, 1 row affected (0.00 sec)

mysql> show databases; / /显示当前存在的数据库，已经没有了数据库b

+--------------------+

| Database |

+--------------------+

| information_schema |

| a |

| c |

| mysql |

| test |

+--------------------+

5 rows in set (0.00 sec)

mysql> source /c_db.sql //恢复/c_db.sql ？？？

Query OK, 0 rows affected (0.00 sec)

Query OK, 1 row affected (0.00 sec)

Database changed

Query OK, 0 rows affected (0.00 sec)

Query OK, 8 rows affected (0.00 sec)

Records: 8 Duplicates: 0 Warnings: 0

Query OK, 0 rows affected (0.00 sec)

mysql> show databases; //恢复成功，再来显示当前存在的数据库，数据库b又回来了

+--------------------+

| Database |

+--------------------+

| information_schema |

| a |

| b |

| c |

| mysql |

| test |

+--------------------+

6 rows in set (0.00 sec)

mysql> show columns from student; //显示表结构（显示每一列）

+-------+-------------+------+-----+---------+-------+

+-------+-------------+------+-----+---------+-------+

+-------+-------------+------+-----+---------+-------+

1 row in set (0.00 sec)

mysql> show processlist; //查看当前连接的人

+----+------+-----------+------+---------+------+-------+------------------+

+----+------+-----------+------+---------+------+-------+------------------+ //只有一个id为11的连接者

+----+------+-----------+------+---------+------+-------+------------------+

1 row in set (0.00 sec)

mysql> kill 11; //删掉id为11的连接者

Query OK, 0 rows affected (0.00 sec)

mysql> show processlist;

ERROR 2006 (HY000): MySQL server has gone away

No connection. Trying to reconnect... //因为只有一个还删了，所以重新分配并连接

Connection id: 12

Current database: b

+----+------+-----------+------+---------+------+-------+------------------+

+----+------+-----------+------+---------+------+-------+------------------+

+----+------+-----------+------+---------+------+-------+------------------+

1 row in set (0.00 sec)

一个实例（包括库的操作和表的操作）：

mysql> create database if not exists bit default character set utf8 collate utf8_general_ci;

//没有简写 character set=charset

Query OK, 1 row affected (0.00 sec)

mysql> show create database bit;

+----------+--------------------------------------------------------------+

| Database | Create Database |

+----------+--------------------------------------------------------------+

| bit | CREATE DATABASE `bit` /*!40100 DEFAULT CHARACTER SET utf8 */ |

//不显示校验规则是因为默认的校验规则就是utf8_general_ci

+----------+--------------------------------------------------------------+

1 row in set (0.00 sec)

mysql> alter table user add column login varchar(32); //给user表加一列login

Query OK, 0 rows affected (0.01 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> desc user; //显示user的属性设置

+----------+-------------+------+-----+---------+-------+

+----------+-------------+------+-----+---------+-------+

| id | int(11) | YES | | NULL | |

+----------+-------------+------+-----+---------+-------+

4 rows in set (0.00 sec)

mysql> insert into user values (1,'bit',md5('123'),'123'); //给user表添加一条信息（采用加密密码）

Query OK, 1 row affected (0.00 sec)

mysql> select * from user; //显示user表中的所有数据

+------+------+----------------------------------+-------+

+------+------+----------------------------------+-------+

| 1 | bit | 202cb962ac59075b964b07152d234b70 | 123 |

+------+------+----------------------------------+-------+

1 row in set (0.00 sec)

mysql> alter table user modify column name varchar(8); //修改user表中name的属性（varchar(32)->varchar(8)）

Query OK, 1 row affected (0.01 sec)

Records: 1 Duplicates: 0 Warnings: 0

mysql> desc user;

+----------+-------------+------+-----+---------+-------+

+----------+-------------+------+-----+---------+-------+

| id | int(11) | YES | | NULL | |

+----------+-------------+------+-----+---------+-------+

4 rows in set (0.00 sec)

mysql> alter table user modify column name varchar(1); //修改user表中name的属性（varchar(8)->varchar(1)）

Query OK, 1 row affected, 1 warning (0.01 sec) //虽然有一条警告，但修改成功

Records: 1 Duplicates: 0 Warnings: 1

mysql> desc user; //没有报错数据库中有信息长于1个字符却没有报错，不正常

+----------+-------------+------+-----+---------+-------+

+----------+-------------+------+-----+---------+-------+

| id | int(11) | YES | | NULL | |

+----------+-------------+------+-----+---------+-------+

4 rows in set (0.00 sec)

mysql> select * from user;

+------+------+----------------------------------+-------+

+------+------+----------------------------------+-------+

| 1 | b | 202cb962ac59075b964b07152d234b70 | 123 | //name=bit被截成name=b

+------+------+----------------------------------+-------+

1 row in set (0.00 sec)

mysql> set sql_mode=strict_trans_tables; //严格校验，报错之前不报错是因为版本低 >5.7.4版本的时候才能开启

Query OK, 0 rows affected (0.00 sec)

mysql> alter table user modify column password varchar(1);

//再修改password为varchar(1)时报错,因为表中已经有md5加密后的密码“123”，长度大于1个字符

ERROR 1265 (01000): Data truncated for column 'password' at row 1

mysql> alter table user drop column name; //删除user表的name列

Query OK, 1 row affected (0.01 sec)

Records: 1 Duplicates: 0 Warnings: 0

mysql> desc user;

+----------+-------------+------+-----+---------+-------+

+----------+-------------+------+-----+---------+-------+

| id | int(11) | YES | | NULL | |

+----------+-------------+------+-----+---------+-------+

3 rows in set (0.00 sec)

mysql> drop table if exists user; //删除user表

Query OK, 0 rows affected (0.00 sec)

mysql> show tables;

Empty set (0.00 sec)

mysql> drop table user; //再删报错（不加if exists）

ERROR 1051 (42S02): Unknown table 'user'

mysql> drop table if exists user;

Query OK, 0 rows affected, 1 warning (0.00 sec) //警告（加上if exists）

mysql> show warnings; //查看警告

+-------+------+----------------------+

| Level | Code | Message |

+-------+------+----------------------+

| Note | 1051 | Unknown table 'user' |

+-------+------+----------------------+

1 row in set (0.00 sec)

mysql> create table user (id int , name varchar(32), login varchar(32), password varchar(32)); //重建user表

Query OK, 0 rows affected (0.01 sec)

mysql> alter table user change column name nick varchar(32); //修改name列的名字为nick

Query OK, 0 rows affected (0.00 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> desc user; //显示表的属性设置修改成功

+----------+-------------+------+-----+---------+-------+

+----------+-------------+------+-----+---------+-------+ //default即默认表示默认值

| id | int(11) | YES | | NULL | |

+----------+-------------+------+-----+---------+-------+

4 rows in set (0.00 sec)

数据类型：

mysql> help data types; //出错

Nothing found

Please try to run 'help contents' for a list of all accessible topics

mysql> help contents; //要先获取目录，再翻到具体的章节

……

mysql> help data types; //再获取data types的帮助

mysql> create table t1 (a int , b bit(8)); //创建t1表 a为int类型，b为bit类型

Query OK, 0 rows affected (0.01 sec)

mysql> insert into t1 values(10,10); //给a 10，给b也是10

Query OK, 1 row affected (0.00 sec)

mysql> select * from t1;

+------+------+

| a | b |

+------+------+ //10是一个不可见的字符（ASSII码）

| 10 |

+------+------+

1 row in set (0.00 sec)

mysql> insert into t1 values(10,65); //65对应字符A

Query OK, 1 row affected (0.00 sec)

mysql> select * from t1;

+------+------+

| a | b |

+------+------+

| 10 |

| 10 | A |

+------+------+

2 rows in set (0.00 sec)

mysql> create table t2 (name bit(65)); //bit类型的最大值为64位

ERROR 1439 (42000): Display width out of range for column 'name' (max = 64)

mysql> create table t3 (a int unsigned , b int unsigned); //设置为无符号int型

Query OK, 0 rows affected (0.01 sec)

mysql> insert into t3 value (1,1); //插入一条数据 a=1，b=1

Query OK, 1 row affected (0.00 sec)

mysql> select * from t3;

+------+------+

| a | b |

+------+------+

| 1 | 1 |

+------+------+

1 row in set (0.00 sec)

mysql> select a-b from t3; //查询a-b的值

+------+

| a-b |

+------+

| 0 |

+------+

1 row in set (0.00 sec)

mysql> insert into t3 value (1,2);

Query OK, 1 row affected (0.00 sec)

mysql> select * from t3;

+------+------+

| a | b |

+------+------+

| 1 | 1 |

| 1 | 2 |

+------+------+

2 rows in set (0.00 sec)

mysql> select a-b from t3; //无符号数类型下，1-2！=-1

+----------------------+

| a-b |

+----------------------+

| 0 |

| 18446744073709551615 |

+----------------------+

2 rows in set (0.00 sec)

mysql> set sql_mode=no_unsigned_subtraction; //为了得到想要的结果，用该命令更改设置

Query OK, 0 rows affected (0.00 sec)

mysql> select * from t3;

+------+------+

| a | b |

+------+------+

| 1 | 1 |

| 1 | 2 |

+------+------+

2 rows in set (0.00 sec)

mysql> select a-b from t3; //得到-1

+------+

| a-b |

+------+

| 0 |

| -1 |

+------+

2 rows in set (0.00 sec)

mysql> insert into t1 values (300,300);

Query OK, 1 row affected, 1 warning (0.00 sec) //给出警告但成功不应该成功，应该报错

mysql> show warnings;

+---------+------+--------------------------------------------+

| Level | Code | Message |

+---------+------+--------------------------------------------+ //越界

| Warning | 1264 | Out of range value for column 'b' at row 1 |

+---------+------+--------------------------------------------+

1 row in set (0.00 sec

mysql> set sql_mode=strict_trans_tables; //防止越界，严格校验，报错

Query OK, 0 rows affected (0.00 sec)

mysql> select * from t1;

+------+------+

| a | b |

+------+------+

| 10 |

| 10 | A |

| 300 | � | //乱码

+------+------+

3 rows in set (0.00 sec)

mysql> insert into t1 values (300,300);

ERROR 1406 (22001): Data too long for column 'b' at row 1 //设置后插入300大小的bit类型，会报错

MySQL第二课（库的操作、表的操作、数据类型）

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