查看已有的数据库：

mysql>show databases;+--------------------+

| Database |

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

| information_schema |

| test |

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

2 rows in set (0.05 sec)

新建数据库语句:

mysql>create database wzu;

Query OK,1 row affected (0.05sec)

mysql>show databases;+--------------------+

| Database |

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

| information_schema |

| test |

| wzu |

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

3 rows in set (0.05 sec)

要对某个数据库进行操作时首先要选中这个数据库,使用use ：

mysql>use wzu

Database changed

创建表格:

命令:create table ＜表名＞ ( ＜属性名　属性类型　［修饰］＞ );

create table student(sno char(9) primary key,sname char(20) unique,ssex char(2),sage smallint, sdept char(20));

create table course(cno char(4) primary key,cname char(40) not null,cpno char(4),ccredit smallint,foreign key(cpno) references course(cno));

create table sc(sno char(9),cno char(4),grade smallint,primary key(sno,cno),foreign key(sno) references student(sno),foreign key(cno) references course(cno));

删除表格:

命令：drop table ＜表名＞;

mysql>drop table emp;Query OK, 0 rows affected (0.41 sec)

查看数据库中有哪些表格:

mysql> show tables;+---------------+

| Tables_in_wzu |

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

| course |

| sc |

| student |

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

更改外键约束:

1 set foreign_key_checks=0; //忽略外键检查

2 set foreign_key_checks=1; //重启外键检查

更改表中某属性的数据类型:

命令:alter table ＜表名＞ modify ＜需要更改的属性＞ ＜想要更改的类型＞；

如:student 表中的sno字段改成varchar(11)

mysql> alter table student modify sno varchar(11);

Query OK,0 rows affected (0.15sec)

Records:0 Duplicates: 0 Warnings: 0

可以用desc ＜表名＞ 来查看表格结构：

mysql>desc student;+-------+-------------+------+-----+---------+-------+

| Field | Type | Null | Key | Default | Extra |

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

| sno | varchar(11) | NO | PRI | | |

| sname | varchar(20) | YES | UNI | NULL | |

| ssex | varchar(2) | YES | | NULL | |

| sage | smallint(6) | YES | | NULL | |

| sdept | varchar(20) | YES | | NULL | |

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

表格插入数据:

命令：insert into values( 填,入,相,应,的,值 );

1 insert into student values('1024','测试','男','18','CS');

删除一行数据:

命令:delete from where [条件];

1 mysql> delete from emp where empno='232';

修改一行数据：

命令：update set [属性名]=[值] [where] [条件]

1 mysql> update course set cpno=null where cpno='NULL';

表格中的简单数据查询:

select * from [表名]

如:select * from student;

* 表示查询表格中所有的列,也可以用列名加','隔开来选择自己需要的数据

mysql> select * fromstudent;+-------------+--------+------+------+-------+

| sno | sname | ssex | sage | sdept |

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

| 1024 | 测试 | 男 | 18 | CS |

| 1621116 | 周帅 | 男 | 21 | CS |

+-------------+--------+------+------+-------+mysql> select sno,sname fromstudent;+-------------+--------+

| sno | sname |

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

| 1024 | 测试 |

| 1621116 | 周帅 |

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

给已创建的表格增加一栏属性:

alter table add ;

如:

mysql> alter table dept add type varchar(11);

Query OK,4 rows affected (0.62sec)

Records:4 Duplicates: 0 Warnings: 0mysql>desc dept;+--------+--------------+------+-----+---------+-------+

| Field | Type | Null | Key | Default | Extra |

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

| deptno | decimal(2,0) | NO | PRI | NULL | |

| dname | varchar(14) | NO | | NULL | |

| loc | varchar(13) | YES | | NULL | |

| type | varchar(11) | YES | | NULL | |

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

在已创建的表格中删除一栏属性:

alter table drop ;

如:

mysql>alter table dept drop type;

Query OK,4 rows affected (0.57sec)

Records:4 Duplicates: 0 Warnings: 0mysql>desc dept;+--------+--------------+------+-----+---------+-------+

| Field | Type | Null | Key | Default | Extra |

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

| deptno | decimal(2,0) | NO | PRI | NULL | |

| dname | varchar(14) | NO | | NULL | |

| loc | varchar(13) | YES | | NULL | |

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

当发现一个操作有warning时 可以通过show warnings；来查看警告信息：

mysql> show warnings;

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

| Level | Code | Message |

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

| Warning | 1366 | Incorrect string value: '\xE6\x9D\x8E\xE5\x8B\x87' for column 'sname' at row 1 |

| Warning | 1366 | Incorrect string value: '\xE7\x94\xB7' for column 'ssex' at row 1 |

| Warning | 1366 | Incorrect string value: '\xE6\x95\xB0\xE6\x8D\xAE...' for column 'cname' at row 1 |

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

此处的问题主要是因为插入的编码格式不兼容(插入的数据编码为utf8 表格的编码为latinl)

mysql查看当前选择的数据库:

mysql> selectdatabase();+------------+

| database() |

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

| groupdb |

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

//或者：

mysql> show tables;

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

| Tables_in_groupdb |//此处为当前数据库

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

| course            |

| dept              |

| emp               |

| jwc               |

| salgrade          |

| sc                |

| student           |

| temp              |

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

//或者：

mysql> status;

--------------

mysql Ver 14.14 Distrib 5.7.14, for Win64 (x86_64)

Connection id: 2721

Current database: groupdb //此处为当前数据库

Current user: group@122.228.131.86

SSL: Not in use

Using delimiter: ;

Server version: 5.5.56-MariaDB MariaDB Server

Protocol version: 10

Connection: AAA.AAA.AAA.AAA via TCP/IP

Server characterset: utf8

Db characterset: utf8

Client characterset: utf8

Conn. characterset: utf8

TCP port: 3306

Uptime: 2 days 5 hours 25 min 51 sec

Threads: 2 Questions: 549 Slow queries: 0 Opens: 26 Flush tables: 2 Open tables: 44 Queries per second avg: 0.002

2018-04-30

判断一个值是否为NULL：

使用 is 关键字而不能用 = 来判断

mysql> select * from course where cpno is null;+-----+--------------+------+---------+

| cno | cname | cpno | ccredit |

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

| 2 | 高等数学 | NULL | 2 |

| 6 | 数据处理 | NULL | 2 |

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

2 rows in set (0.05sec)

mysql> select * from course where cpno is not null;+-----+--------------+------+---------+

| cno | cname | cpno | ccredit |

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

| 1 | 数据库 | 5 | 4 |

| 3 | 信息系统 | 1 | 4 |

| 4 | 操作系统 | 6 | 3 |

| 5 | 数据结构 | 7 | 4 |

| 7 | C语言 | 6 | 4 |

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