MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

时间:2022-05-29 00:31:55

0、唯一索引

 MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

  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

 

 MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

 上面为联合索引:num和xx不能完全一样

MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

 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

MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

  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

 MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

 

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
MySQL之唯一索引、外键的变种、SQL语句数据行操作补充 

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
MySQL之唯一索引、外键的变种、SQL语句数据行操作补充
MySQL之唯一索引、外键的变种、SQL语句数据行操作补充   

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‘);
MySQL之唯一索引、外键的变种、SQL语句数据行操作补充   
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);

 MySQL之唯一索引、外键的变种、SQL语句数据行操作补充 

分组:

max:
MySQL之唯一索引、外键的变种、SQL语句数据行操作补充
#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: MySQL之唯一索引、外键的变种、SQL语句数据行操作补充 此外还有min、sum、avg

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:
MySQL之唯一索引、外键的变种、SQL语句数据行操作补充 
也可以用where,但后面不能加聚合函数
MySQL之唯一索引、外键的变种、SQL语句数据行操作补充 

 连表操作:

MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

 

 做法:select * from userinfo5,department5 where userinfo5.part_id = department5.id

 MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

 

 推荐下面写法:

MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

 

 (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

 MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

 

   (2) select * from userinfo5 right join department5 on userinfo5.part_id = department5.id;    #department5右边全部显示

MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

 

(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

 MySQL之唯一索引、外键的变种、SQL语句数据行操作补充

 

作业练习:http://www.cnblogs.com/wupeiqi/articles/5729934.html