阅读目录
引擎介绍
mysql中的存储引擎(https://www.cnblogs.com/l-hf/p/11533999.html)
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(https://www.cnblogs.com/l-hf/p/11532788.html)
表的完整性约束
mysql表的完整性约束(https://www.cnblogs.com/l-hf/p/11534027.html)
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。