MySQL表操作

引擎介绍

mysql中的存储引擎

表介绍

表就相当于文件,表中的一条记录就相当于文件的一行内容,不同的是,表中的一条记录有对应的标题,称为表的字段

还记得我们之前写过的‘员工信息表作业’么?存储这员工信息的文件是这样的:

id,name,age,sex,phone,job
1,Alex,83,female,13651054608,IT
2,Egon,26,male,13304320533,Tearcher
3,nezha,25,male,13332353222,IT
4,boss_jin,40,male,13332353333,IT

如果把上面这个文件改成一张表,应该是下面这个样子

id name age sex phone job
1 Alex 83 female 13651054608 IT
2 Egon 26 male 13304320533 Teacher
3 nezha 25 male 13332353222 IT
4 boss_jin 40 male 13332353333 IT
id,name,age,sex,phone,job称为字段,其余的,一行内容称为一条记录 

创建表

#语法:
create table 表名(
字段名1 类型[(宽度) 约束条件],
字段名2 类型[(宽度) 约束条件],
字段名3 类型[(宽度) 约束条件]
);

#注意:
1. 在同一张表中,字段名是不能相同
2. 宽度和约束条件可选
3. 字段名和类型是必须的
mysql> create database staff;
Query OK, 1 row affected (0.00 sec)

mysql> use staff;
Database changed
mysql> create table staff_info (id int,name varchar(50),age int(3),sex enum('male','female'),phone bigint(11),job varchar(11));
Query OK, 0 rows affected (0.02 sec)


mysql> show tables;
+-----------------+
| Tables_in_staff |
+-----------------+
| staff_info      |
+-----------------+
1 row in set (0.00 sec)

mysql> desc staff_info;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(11)               | YES  |     | NULL    |       |
| name  | varchar(50)           | YES  |     | NULL    |       |
| age   | int(3)                | YES  |     | NULL    |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mysql> select id,name,sex from staff_info;
Empty set (0.00 sec)

mysql> select * from staff_info;
Empty set (0.00 sec)
mysql> insert into staff_info (id,name,age,sex,phone,job) values (1,'Alex',83,'female',13651054608,'IT');
Query OK, 1 row affected (0.00 sec)

mysql> insert into staff_info values (2,'Egon',26,'male',13304320533,'Teacher');
Query OK, 1 row affected (0.00 sec)

mysql> insert into staff_info values (3,'nezha',25,'male',13332353222,'IT'),(4,'boss_jin',40,'male',13332353333,'IT');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from staff_info;
+------+----------+------+--------+-------------+---------+
| id   | name     | age  | sex    | phone       | job     |
+------+----------+------+--------+-------------+---------+
|    1 | Alex     |   83 | female | 13651054608 | IT      |
|    2 | Egon     |   26 | male   | 13304320533 | Teacher |
|    3 | nezha    |   25 | male   | 13332353222 | IT      |
|    4 | boss_jin |   40 | male   | 13332353333 | IT      |
+------+----------+------+--------+-------------+---------+
4 rows in set (0.00 sec)

查看表结构

查看表结构有两种方式:

describe [tablename];这种方法和desc [tablename];效果相同;可以查看当前的表结构

虽然desc命令可以查看表的定义,但是其输出的信息还不够全面,为了得到更全面的表定义信息,有时候就需要查看创建表的SQL语句,使用show create table语法。除了可以看到表定义之外,还可以看到engine(存储引擎)和charset(字符集)等信息。(\G选项的含义是是的记录能够竖向排列,以便更好的显示内容较长的记录。)

mysql> describe staff_info;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(11)               | YES  |     | NULL    |       |
| name  | varchar(50)           | YES  |     | NULL    |       |
| age   | int(3)                | YES  |     | NULL    |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mysql> desc staff_info;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(11)               | YES  |     | NULL    |       |
| name  | varchar(50)           | YES  |     | NULL    |       |
| age   | int(3)                | YES  |     | NULL    |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mysql> show create table staff_info\G;
*************************** 1. row ***************************
       Table: staff_info
Create Table: CREATE TABLE `staff_info` (
  `id` int(11) DEFAULT NULL,
  `name` varchar(50) DEFAULT NULL,
  `age` int(3) DEFAULT NULL,
  `sex` enum('male','female') DEFAULT NULL,
  `phone` bigint(11) DEFAULT NULL,
  `job` varchar(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.01 sec)

ERROR: 
No query specified

mysql中的数据类型

mysql支持的数据类型

表的完整性约束

mysql表的完整性约束

修改表结构

语法:
1. 修改表名
      ALTER TABLE 表名 
                      RENAME 新表名;

2. 增加字段
      ALTER TABLE 表名
                      ADD 字段名  数据类型 [完整性约束条件…],
                      ADD 字段名  数据类型 [完整性约束条件…];
                            
3. 删除字段
      ALTER TABLE 表名 
                      DROP 字段名;

4. 修改字段
      ALTER TABLE 表名 
                      MODIFY  字段名 数据类型 [完整性约束条件…];
      ALTER TABLE 表名 
                      CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…];
      ALTER TABLE 表名 
                      CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…];

5.修改字段排列顺序/在增加的时候指定字段位置
    ALTER TABLE 表名
                     ADD 字段名  数据类型 [完整性约束条件…]  FIRST;
    ALTER TABLE 表名
                     ADD 字段名  数据类型 [完整性约束条件…]  AFTER 字段名;
    ALTER TABLE 表名
                     CHANGE 字段名  旧字段名 新字段名 新数据类型 [完整性约束条件…]  FIRST;
    ALTER TABLE 表名
                     MODIFY 字段名  数据类型 [完整性约束条件…]  AFTER 字段名;
create table t(id int unique,name char(10) not null);

#去掉null约束
alter table t modify name char(10) null;
# 添加null约束
alter table t modify name char(10) not null;


# 去掉unique约束
alter table t drop index id;
# 添加unique约束
alter table t modify id int unique;

alter处理null和unique约束
1、首先创建一个数据表table_test:
create table table_test(
`id` varchar(100) NOT NULL,
`name` varchar(100) NOT NULL,
PRIMARY KEY (`name`)
); 
2、如果发现主键设置错了,应该是id是主键,但如今表里已经有好多数据了,不能删除表再重建了,仅仅能在这基础上改动表结构。
先删除主键
alter table table_test drop primary key;
然后再增加主键
alter table table_test add primary key(id);
注:在增加主键之前,必须先把反复的id删除掉。
创建press表
CREATE TABLE `press` (
  `id` int(11) NOT NULL,
  `name` char(10) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ;

创建book表
CREATE TABLE `book` (
  `id` int(11) DEFAULT NULL,
  `bk_name` char(12) DEFAULT NULL,
  `press_id` int(11) NOT NULL,
  KEY `press_id` (`press_id`)
) ;

为book表添加外键
alter table book add constraint fk_id foreign key(press_id) references press(id);

删除外键
alter table book drop foreign key fk_id;
mysql> desc staff_info;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(11)               | YES  |     | NULL    |       |
| name  | varchar(50)           | YES  |     | NULL    |       |
| age   | int(3)                | YES  |     | NULL    |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

# 表重命名
mysql> alter table staff_info rename staff;
Query OK, 0 rows affected (0.00 sec)

mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(11)               | YES  |     | NULL    |       |
| name  | varchar(50)           | YES  |     | NULL    |       |
| age   | int(3)                | YES  |     | NULL    |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

# 删除sex列
mysql> alter table staff drop sex;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc staff;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(50) | YES  |     | NULL    |       |
| age   | int(3)      | YES  |     | NULL    |       |
| phone | bigint(11)  | YES  |     | NULL    |       |
| job   | varchar(11) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
5 rows in set (0.01 sec)

# 添加列
mysql> alter table staff add sex enum('male','female');
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

# 修改id的宽度
mysql> alter table staff modify id int(4);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(4)                | YES  |     | NULL    |       |
| name  | varchar(50)           | YES  |     | NULL    |       |
| age   | int(3)                | YES  |     | NULL    |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.01 sec)

# 修改name列的字段名
mysql> alter table staff change name sname varchar(20);
Query OK, 4 rows affected (0.03 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(4)                | YES  |     | NULL    |       |
| sname | varchar(20)           | YES  |     | NULL    |       |
| age   | int(3)                | YES  |     | NULL    |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

# 修改sex列的位置
mysql> alter table staff modify sex enum('male','female') after sname;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(4)                | YES  |     | NULL    |       |
| sname | varchar(20)           | YES  |     | NULL    |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
| age   | int(3)                | YES  |     | NULL    |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

# 创建自增id主键
mysql> alter table staff modify id int(4) primary key auto_increment;
Query OK, 4 rows affected (0.02 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> desc staff;
+-------+-----------------------+------+-----+---------+----------------+
| Field | Type                  | Null | Key | Default | Extra          |
+-------+-----------------------+------+-----+---------+----------------+
| id    | int(4)                | NO   | PRI | NULL    | auto_increment |
| sname | varchar(20)           | YES  |     | NULL    |                |
| sex   | enum('male','female') | YES  |     | NULL    |                |
| age   | int(3)                | YES  |     | NULL    |                |
| phone | bigint(11)            | YES  |     | NULL    |                |
| job   | varchar(11)           | YES  |     | NULL    |                |
+-------+-----------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

# 删除主键,可以看到删除一个自增主键会报错
mysql> alter table staff drop primary key;
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

# 需要先去掉主键的自增约束,然后再删除主键约束
mysql> alter table staff modify id int(11);
Query OK, 4 rows affected (0.02 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(11)               | NO   | PRI | 0       |       |
| sname | varchar(20)           | YES  |     | NULL    |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
| age   | int(3)                | YES  |     | NULL    |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.01 sec)

mysql> alter table staff drop primary key;
Query OK, 4 rows affected (0.06 sec)
Records: 4  Duplicates: 0  Warnings: 0

# 添加联合主键
mysql> alter table staff add primary key (sname,age);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

# 删除主键
mysql> alter table staff drop primary key;
Query OK, 4 rows affected (0.02 sec)
Records: 4  Duplicates: 0  Warnings: 0

# 创建主键id
mysql> alter table staff add primary key (id);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc staff;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type                  | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id    | int(11)               | NO   | PRI | 0       |       |
| sname | varchar(20)           | NO   |     |         |       |
| sex   | enum('male','female') | YES  |     | NULL    |       |
| age   | int(3)                | NO   |     | 0       |       |
| phone | bigint(11)            | YES  |     | NULL    |       |
| job   | varchar(11)           | YES  |     | NULL    |       |
+-------+-----------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

# 为主键添加自增属性
mysql> alter table staff modify id int(4) auto_increment;
Query OK, 4 rows affected (0.02 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> desc staff;
+-------+-----------------------+------+-----+---------+----------------+
| Field | Type                  | Null | Key | Default | Extra          |
+-------+-----------------------+------+-----+---------+----------------+
| id    | int(4)                | NO   | PRI | NULL    | auto_increment |
| sname | varchar(20)           | NO   |     |         |                |
| sex   | enum('male','female') | YES  |     | NULL    |                |
| age   | int(3)                | NO   |     | 0       |                |
| phone | bigint(11)            | YES  |     | NULL    |                |
| job   | varchar(11)           | YES  |     | NULL    |                |
+-------+-----------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

删除表

DROP TABLE 表名;

多表结构的创建与分析

如何找出两张表之间的关系

分析步骤:
#1、先站在左表的角度去找
是否左表的多条记录可以对应右表的一条记录,如果是,则证明左表的一个字段foreign key 右表一个字段(通常是id)

#2、再站在右表的角度去找
是否右表的多条记录可以对应左表的一条记录,如果是,则证明右表的一个字段foreign key 左表一个字段(通常是id)

#3、总结:
#多对一:
如果只有步骤1成立,则是左表多对一右表
如果只有步骤2成立,则是右表多对一左表

#多对多
如果步骤1和2同时成立,则证明这两张表时一个双向的多对一,即多对多,需要定义一个这两张表的关系表来专门存放二者的关系

#一对一:
如果1和2都不成立,而是左表的一条记录唯一对应右表的一条记录,反之亦然。这种情况很简单,就是在左表foreign key右表的基础上,将左表的外键字段设置成unique即可

建立表之间的关系

#一对多或称为多对一
三张表:出版社,作者信息,书

一对多(或多对一):一个出版社可以出版多本书

关联方式:foreign key

=====================多对一=====================
create table press(
id int primary key auto_increment,
name varchar(20)
);

create table book(
id int primary key auto_increment,
name varchar(20),
press_id int not null,
foreign key(press_id) references press(id)
on delete cascade
on update cascade
);


insert into press(name) values
('北京工业地雷出版社'),
('人民音乐不好听出版社'),
('知识产权没有用出版社')
;

insert into book(name,press_id) values
('九阳神功',1),
('九阴真经',2),
('九阴白骨爪',2),
('独孤九剑',3),
('降龙十巴掌',2),
('葵花宝典',3)
;

班级和学生
一个班级可以对应多个学生,但一个学生只能对应一个班级

主机和机房
一个机房可以有多台主机,但是一个主机只能属于一个机房

#多对多
三张表:出版社,作者信息,书

多对多:一个作者可以写多本书,一本书也可以有多个作者,双向的一对多,即多对多
  
关联方式:foreign key+一张新的表

=====================多对多=====================
create table author(
id int primary key auto_increment,
name varchar(20)
);


#这张表就存放作者表与书表的关系,即查询二者的关系查这表就可以了
create table author2book(
id int not null unique auto_increment,
author_id int not null,
book_id int not null,
constraint fk_author foreign key(author_id) references author(id)
on delete cascade
on update cascade,
constraint fk_book foreign key(book_id) references book(id)
on delete cascade
on update cascade,
primary key(author_id,book_id)
);


#插入四个作者,id依次排开
insert into author(name) values('egon'),('alex'),('yuanhao'),('wpq');

#每个作者与自己的代表作如下
egon: 
九阳神功
九阴真经
九阴白骨爪
独孤九剑
降龙十巴掌
葵花宝典
alex: 
九阳神功
葵花宝典
yuanhao:
独孤九剑
降龙十巴掌
葵花宝典
wpq:
九阳神功


insert into author2book(author_id,book_id) values
(1,1),
(1,2),
(1,3),
(1,4),
(1,5),
(1,6),
(2,1),
(2,6),
(3,4),
(3,5),
(3,6),
(4,1)
;

服务和机器
一个服务可能被部署到多台机器上,一台机器上也可以部署多个服务

学生和课程
一个学生可以选择多门课程,一门课程也可以被多个学生选择

#一对一
两张表:学生表和客户表

一对一:一个学生是一个客户

关联方式:foreign key+unique

create table customer(
    -> id int primary key auto_increment,
    -> name varchar(20) not null,
    -> qq varchar(10) not null,
    -> phone char(16) not null
    -> );

create table student(
    -> id int primary key auto_increment,
    -> class_name varchar(20) not null,
    -> customer_id int unique, #该字段一定要是唯一的
    -> foreign key(customer_id) references customer(id) #外键的字段一定要保证unique
    -> on delete cascade
    -> on update cascade
    -> );

#增加客户
mysql> insert into customer(name,qq,phone) values
    -> ('韩蕾','31811231',13811341220),
    -> ('杨澜','123123123',15213146809),
    -> ('翁惠天','283818181',1867141331),
    -> ('杨宗河','283818181',1851143312),
    -> ('袁承明','888818181',1861243314),
    -> ('袁清','112312312',18811431230)

mysql> #增加学生
mysql> insert into student(class_name,customer_id) values
    -> ('脱产1班',3),
    -> ('周末1期',4),
    -> ('周末1期',5)
    -> ;

例一:一个用户只有一个博客

    用户表:
    id  name
    1    egon
    2    alex
    3    wupeiqi


    博客表   
           fk+unique
    id url name_id
    1  xxxx   1
    2  yyyy   3
    3  zzz    2



例二:一个管理员唯一对应一个用户
    用户表:
    id user  password
    1  egon    xxxx
    2  alex    yyyy

    管理员表:
       fk+unique
    id user_id password
    1   1      xxxxx
    2   2      yyyyy

作业

根据表结构合理设计表与表之间的主外键关系和约束,并完成表结构的创建。

img

posted @ 2019-08-27 23:08  changxin7  阅读(153)  评论(0编辑  收藏