0、唯一索引
unique对num进行唯一限制，表示num是独一无二的，uql是唯一索引名称
上面为联合索引：num和xx不能完全一样
1、外键的变种
a. 用户表和部门表
用户：
1 alex 1
2 root 1
3 egon 2
4 laoyao 3
部门:
1 服务
2 保安
3 公关
===》 一对多
b. 用户表和博客表
用户表：
1 alex
2 root
3 egon
4 laoyao
博客表：
FK() 唯一
1 /yuanchenqi/ 4
2 /alex3714/ 1
3 /asdfasdf/ 3
4 /ffffffff/ 2
===> 一对一
程序代码：
create table userinfo1( id int auto_increment primary key, name char(10), gender char(10), email varchar(64) )engine=innodb default charset=utf8;
create table admin( id int not null auto_increment primary key, username varchar(64) not null, password VARCHAR(64) not null, user_id int not null, unique uq_u1 (user_id), CONSTRAINT fk_admin_u1 FOREIGN key (user_id) REFERENCES userinfo1(id) )engine=innodb default charset=utf8;
c.多对多
create table userinfo2( id int auto_increment primary key, name char(10), gender char(10), email varchar(64) )engine=innodb default charset=utf8; create table host( id int auto_increment primary key, hostname char(64) )engine=innodb default charset=utf8; create table user2host( id int auto_increment primary key, userid int not null, hostid int not null, unique uq_user_host (userid,hostid), CONSTRAINT fk_u2h_user FOREIGN key (userid) REFERENCES userinfo2(id), CONSTRAINT fk_u2h_host FOREIGN key (hostid) REFERENCES host(id) )engine=innodb default charset=utf8;
3、SQL语句数据行操作补充
3.1 增
insert into tb11(name,age) values(‘alex‘,12); #往tb11中插入一条数据 insert into tb11(name,age) values(‘alex‘,12),(‘root‘,18); #往tb11中插入多条数据 insert into tb12(name,age) select name,age from tb11; #把tb11中的数据复制到tb12中
3.2 删
delete from tb12; delete from tb12 where id !=2 delete from tb12 where id =2 delete from tb12 where id > 2 delete from tb12 where id >=2 delete from tb12 where id >=2 or name=‘alex‘
3.3 改
update tb12 set name=‘alex‘ where id>12 and name=‘xx‘ update tb12 set name=‘alex‘,age=19 where id>12 and name=‘xx‘
3.4 查
select * from tb12; select id,name from tb12; select id,name from tb12 where id > 10 or name =‘xxx‘; select name as cname,age from tb12; #查数据，并把表头的name改为cname select id,name as cname from tb12 where id > 10 or name =‘xxx‘; select name,age,11 from tb12; #多出一列，数据全部为11
其他：
select * from tb12 where id != 1 select * from tb12 where id in (1,5,12); #取id为1、5、12的数据 select * from tb12 where id not in (1,5,12); #取id不为1、5、12的数据 select * from tb12 where id in (select id from tb11) #先把tb11的id取出来，作为tb12要查的id select * from tb12 where id between 5 and 12; #取id为5到12的数据（闭区间）
通配符：
select * from tb12 where name like "a%" #查name以a为开头的数据 select * from tb12 where name like "%a%" #查name中带a的数据 select * from tb12 where name like "a_" #查name以a开头，后面只带一位的数据，比如 ab、ag
分页：
select * from tb12 limit 10; #查看前10条 select * from tb12 limit 0,10; #从第0行开始读取，读取10行； select * from tb12 limit 10,10; #从第10行开始读取，读取10行； select * from tb12 limit 20,10; #从第20行开始读取，读取10行； select * from tb12 limit 10 offset 20; #从第20行开始读取，读取10行； #结合Python分页： page = input(‘请输入要查看的页码‘) page = int(page) (page-1) * 10 select * from tb12 limit 0,10; #查看第1页数据 select * from tb12 limit 10,10;2 #查看第2页数据
排序：
select * from tb12 order by id desc; #id从大到小排 select * from tb12 order by id asc; #id从小到大排 select * from tb12 order by age desc,id desc; #age从大到小排，id从大到小排（如果age数相同，就按照id从大到小排） select * from tb12 order by id desc limit 10; #取后10条数据
创建部门与员工表：
create table department5(
id int auto_increment primary key,
title varchar(32)
)engine=innodb default charset=utf8;
insert into department5(title) values(‘经理‘),(‘销售‘),(‘管理‘),(‘财务‘);
create table userinfo5( id int auto_increment primary key, name varchar(32), part_id int, CONSTRAINT fk_user_part FOREIGN key (part_id) REFERENCES department5(id) )engine=innodb default charset=utf8;
insert into userinfo5(name,part_id) values(‘杨涵‘,2),(‘大波‘,1),(‘高月‘,2),(‘送气‘,3),(‘小白‘,4);
分组：
max:#按par_id进行分类，如果part_id相同，就取id最大的那个进行分类
count:
如果对于聚合函数结果进行二次筛选时？必须使用having 例如果想筛选出id大于1的part_id:
也可以用where，但后面不能加聚合函数
连表操作：
做法：select * from userinfo5,department5 where userinfo5.part_id = department5.id
推荐下面写法：
（1）select * from userinfo5 left join department5 on userinfo5.part_id = department5.id; #userinfo5左边全部显示，因为userinfo5中没有对应department5中的刘洋，所以不显示刘洋
(2) select * from userinfo5 right join department5 on userinfo5.part_id = department5.id; #department5右边全部显示
（3）select * from userinfo5 innder join department5 on userinfo5.part_id = department5.id; #将出现null时的一行隐藏
（4）select count(id) from userinfo5; #统计userinfo5中的数据个数
