day23-必备SQL和表关系及授权
1. 必备SQL语句上一节讲解了最基础SQL语句：增删改查，其实在日常的开发中还有很多必备的SQL语句。
这一部分的SQL语句都是围绕着对 表中的数据进行操作的。
提示：今天的所有操作我都只会在 MySQL自带的客户端工具上进行操作。
例如：现在创建如下两张表。
create database day26db default charset utf8 collate utf8_general_ci;create table depart(
id int not null auto_increment primary key,
title varchar(16) not null
)default charset=utf8;
create table info(
id int not null auto_increment primary key,
name varchar(16) not null,
email varchar(32) not null,
age int,
depart_id int
)default charset=utf8;insert into depart(title) values("开发"),("运营"),("销售");
insert into info(name,email,age,depart_id) values("武沛齐","wupeiqi@live.com",19,1);
insert into info(name,email,age,depart_id) values("于超","pyyu@live.com",49,1);
insert into info(name,email,age,depart_id) values("alex","alex@live.com",9,2);
insert into info(name,email,age,depart_id) values("tony","tony@live.com",29,1);
insert into info(name,email,age,depart_id) values("kelly","kelly@live.com",99,3);
insert into info(name,email,age,depart_id) values("james","james@live.com",49,1);
insert into info(name,email,age,depart_id) values("李杰","lijie@live.com",49,1);1.1 条件
根据条件搜索结果。
select * from info where age > 30;
select * from info where id > 1;
select * from info where id = 1;
select * from info where id >= 1;
select * from info where id != 1;
select * from info where id between 2 and 4; -- id大于等于2、且小于等于4
select * from info where name = '武沛齐' and age = 19;
select * from info where name = 'alex' or age = 49;
select * from info where (name = '李杰' or email="pyyu@live.com")and age=49;
select * from info where id in (1,4,6);
select * from info where id not in (1,4,6);
select * from info where id in (select id from depart);
# select * from info where id in (1,2,3);
# exists select * from depart where id=5，去查数据是否存在，如果存在，如果不存在。
select * from info where exists (select * from depart where id=5);
select * from info where not exists (select * from depart where id=5);
select * from (select * from info where id>2) as T where age > 10;select * from info where info.id > 10;
select * from info where id > 10;1.2 通配符
一般用于模糊搜索。
# % 可以匹配任意长度字符
select * from info where name like "%沛%";
select * from info where name like "%沛";
select * from info where email like "%@live.com";
select * from info where name like "武%齐";
select * from info where name like "k%y";
select * from info where email like "wupeiqi%";
# _ 匹配单个字符，不能多也不能少
select * from info where email like "_@live.com";
select * from info where email like "_upeiqi@live.com";
select * from info where email like "__peiqi@live.com";
select * from info where email like "__peiqi_live.co_";注意：数量少，数据量大的搜索。
1.3 映射
想要获取的列。
select * from info;
select id, name from info;
select id, name as NM from info;
select id, name as NM, 123from info;
注意：少些select * ,自己需求。
select
id,
name,
666 as num,
( select max(id) from depart ) as mid, -- max/min/sum
( select min(id) from depart) as nid, -- max/min/sum
age
from info;select
id,
name,
( select title from depart where depart.id=info.depart_id) as x1
from info;
# 注意：效率很低
select
id,
name,
( select title from depart where depart.id=info.depart_id) as x1,
( select title from depart where depart.id=info.id) as x2
from info;select
id,
name,
case depart_id when 1 then "第1部门" end v1
from info;
select
id,
name,
case depart_id when 1 then "第1部门" else "其他" end v2
from info;
select
id,
name,
case depart_id when 1 then "第1部门" end v1,
case depart_id when 1 then "第1部门" else "其他" end v2,
case depart_id when 1 then "第1部门" when 2 then "第2部门" else "其他" end v3,
case when age<18 then "少年" end v4,
case when age<18 then "少年" else "油腻男" end v5,
case when age<18 then "少年" when age<30 then "青年" else "油腻男" end v6
from info;select * from info order by age desc; -- 倒序
select * from info order by age asc;-- 顺序
select * from info order by id desc;
select * from info order by id asc;
select * from info order by age asc,id desc; -- 优先按照age从小到大；如果age相同则按照id从大到小。
select * from info where id>10 order by age asc,id desc;
select * from info where id>6 or name like "%y" order by age asc,id desc;select * from info limit 5; -- 获取前5条数据
select * from info order by id desc limit 3; -- 先排序，再获取前3条数据
select * from info where id > 4 order by id desc limit 3; -- 先排序，再获取前3条数据
select * from info limit 3 offset 2; -- 从位置2开始，向后获取前3数据select age,max(id),min(id),count(id),sum(id),avg(id) from info group by age;select age,count(1) from info group by age;select depart_id,count(id) from info group by depart_id;select depart_id,count(id) from info group by depart_id having count(id) > 2;1.7 左右连表
多个表可以连接起来进行查询。
展示用户信息&部门名称：
select count(id) from info;
select max(id) from info;select age,max(id),min(id),sum(id),count(id) from info group by age;select age,name from info group by age;-- 不建议
select * from info where id in (select max(id) from info group by age);select age,count(id) from info group by age having count(id) > 2;
select age,count(id) from info where id > 4 group by age having count(id) > 2;-- 聚合条件放在having后面到目前为止SQL执行顺序：
where
group by
having
order by
limit 为了更加直接的查看效果，我们分别在 depart 表 和 info 中额外插入一条数据。
select age,count(id) from info where id > 2 group by age having count(id) > 1 order by age desc limit 1;
- 要查询的表info
- 条件 id>2
- 根据age分组
- 对分组后的数据再根据聚合条件过滤 count(id)>1
- 根据age从大到小排序
- 获取第1条这样一来主从表就有区别：
[*]info主表，就以info数据为主，depart为辅。
select age,name from info group by age;-- 不建议
select * from info where id in (select max(id) from info group by age);
[*]depart主表，就以depart数据为主，info为辅。
到目前为止SQL执行顺序：
where
group by
having
order by
limit
select info.id,info.name,info.email,depart.title from info left outer join depart on info.depart_id = depart.id;简写：select * from depart left join info on ....
从表 right outer join 主表 on 主表.x = 从表.idselect info.id,info.name,info.email,depart.title from info right outer join depart on info.depart_id = depart.id;写在最后：多张表也可以连接。
1.8 联合
insert into depart(title) values("运维");select info.id,info.name,info.email,depart.title from info left outer join depart on info.depart_id = depart.id;select info.id,info.name,info.email,depart.title from info right outer join depart on info.depart_id = depart.id;小结
到目前为止，你已经掌握了如下相关指令（SQL语句）：
[*]数据库
[*]数据表
[*]数据行
[*]增加
[*]删除
[*]修改
[*]查询（各种变着花样的查询）
2.表关系
在开发项目时，需要根据业务需求去创建很多的表结构，以此来实现业务逻辑，一般表结构有三类：
[*]单表，单独一张表就可以将信息保存。
[*]一对多，需要两张表来存储信息，且两张表存在 一对多 或 多对一关系。
[*]多对多，需要三张表来存储信息，两张单表 + 关系表，创造出两个单表之间多对多关系。
在上述的表：一对多的 info.depart_id字段、多对多的 boy_girl.boy_id 、girl_id 直接用整型存储就可以，因为他们只要存储关联表的主键ID即可。
在开发中往往还会为他们添加一个 外键约束，保证某一个列的值必须是其他表中的特定列已存在的值，例如：info.depart_id的值必须是 depart.id中已存在的值。
一对多示例：
select * from info left outer join depart on ....
select * from depart left outer join info on ....如果表结构已创建好了，额外想要增加外键：
-- 内连接: 表inner join 表on 条件
select * from info inner join depart on info.depart_id=depart.id;
+----+-----------+------------------+------+-----------+----+--------+
| id | name | email | age| depart_id | id | title|
+----+-----------+------------------+------+-----------+----+--------+
|1 | 武沛齐 | wupeiqi@live.com | 19 | 1 |1 | 开发 |
|2 | 于超 | pyyu@live.com | 49 | 1 |1 | 开发 |
|3 | alex | alex@live.com | 9 | 2 |2 | 运营 |
|4 | tony | tony@live.com | 29 | 1 |1 | 开发 |
|5 | kelly | kelly@live.com | 99 | 3 |3 | 销售 |
|6 | james | james@live.com | 49 | 1 |1 | 开发 |
|7 | 李杰 | lijie@live.com | 49 | 1 |1 | 开发 |
+----+-----------+------------------+------+-----------+----+--------+删除外键：
到目前为止SQL执行顺序：
join
on
where
group by
having
order by
limit 多对多示例：
select id,title from depart
union
select id,name from info;
select id,title from depart
union
select email,name from info;
-- 列数需相同如果表结构已创建好了，额外想要增加外键：
select id from depart
union
select id from info;
-- 自动去重删除外键：
select id from depart
union all
select id from info;
-- 保留所有在以后项目开发时，设计表结构及其关系的是一个非常重要的技能。一般项目开始开发的步骤：
[*]需求调研
[*]设计数据库表结构（根据需求）
[*]项目开发（写代码）
大量的工作应该放在前2个步骤，前期的设计完成之后，后续的功能代码开发就比较简单了。
案例：简易版路飞学城
create table depart(
id int not null auto_increment primary key,
title varchar(16) not null
)default charset=utf8;
create table info(
id int not null auto_increment primary key,
name varchar(16) not null,
email varchar(32) not null,
age int,
depart_id int not null,
constraint fk_info_depart foreign key (depart_id) references depart(id)
)default charset=utf8;alter table info add constraint fk_info_depart foreign key info(depart_id) references depart(id);alter table info drop foreign key fk_info_depart;create table boy(
id int not null auto_increment primary key,
name varchar(16) not null
)default charset=utf8;
create table girl(
id int not null auto_increment primary key,
name varchar(16) not null
)default charset=utf8;
create table boy_girl(
id int not null auto_increment primary key,
boy_id int not null,
girl_id int not null,
constraint fk_boy_girl_boy foreign key boy_girl(boy_id) references boy(id),
constraint fk_boy_girl_girl foreign key boy_girl(girl_id) references girl(id)
)default charset=utf8;3. 授权
之前我们无论是基于Python代码 or 自带客户端 去连接MySQL时，均使用的是 root 账户，拥有对MySQL数据库操作的所有权限。
如果有多个程序的数据库都放在同一个MySQL中，如果程序都用root账户就存在风险了。
这种情况怎么办呢？
在MySQL中支持创建账户，并给账户分配权限，例如：只拥有数据库A操作的权限、只拥有数据库B中某些表的权限、只拥有数据库B中某些表的读权限等。
3.1 用户管理
在MySQL的默认数据库 mysql 中的 user 表中存储着所有的账户信息（含账户、权限等）。
alter table boy_girl add constraint fk_boy_girl_boy foreign key boy_girl(boy_id) references boy(id);
alter table boy_girl add constraint fk_boy_girl_girl foreign key boy_girl(girl_id) references girl(id);
[*]创建和删除用户
alter table info drop foreign key fk_boy_girl_boy;
alter table info drop foreign key fk_boy_girl_girl;create database luffy default charset utf8 collate utf8_general_ci;
use luffy;
[*]修改用户
create table info(
id int not null auto_increment primary key,
username varchar(16) not null,
mobile char(11) not null,
password varchar(64) not null
)default charset=utf8;create table course(
id int not null auto_increment primary key,
title varchar(16) not null
)default charset=utf8;
create table module(
id int not null auto_increment primary key,
title varchar(16) not null,
course_id int not null,
constraint fk_module_course foreign key (course_id) references course(id)
)default charset=utf8;
create table day(
id int not null auto_increment primary key,
title varchar(16) not null,
module_id int not null,
constraint fk_day_module foreign key (module_id) references module(id)
)default charset=utf8;
create table video(
id int not null auto_increment primary key,
title varchar(16) not null,
day_id int not null,
constraint fk_video_day foreign key (day_id) references day(id)
)default charset=utf8;
[*]修改密码
create table module_record(
id int not null auto_increment primary key,
user_id int not null,
module_id int not null,
constraint fk_user_id foreign key module_record(user_id) references info(id),
constraint fk_module_id foreign key module_record(module_id) references module(id)
)default charset=utf8;mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| day26 |
| mysql |
| performance_schema |
| sys |
+--------------------+
10 rows in set (0.00 sec)
mysql> select user,authentication_string,host frommysql.user;
+----------------------------------+-------------------------------------------+-------------------------------+
| user | authentication_string | host |
+----------------------------------+-------------------------------------------+-------------------------------+
| root | *FAAFFE644E901CFAFAEC7562415E5FAEC243B8B2 | localhost |
| mysql.session | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE | localhost |
| mysql.sys | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE | localhost |
+----------------------------------+-------------------------------------------+-------------------------------+
3 rows in set (0.00 sec)
3.2 授权管理
创建好用户之后，就可以为用户进行授权了。
<ul>授权
create user '用户名'@'连接者的IP地址' identified by '密码';create user wupeiqi1@127.0.0.1 identified by 'root123';
drop user wupeiqi1@127.0.0.1;
create user wupeiqi2@'127.0.0.%' identified by 'root123';
drop user wupeiqi2@'127.0.0.%';
create user wupeiqi3@'%' identified by 'root123';
drop user wupeiqi3@'%';
create user 'wupeiqi4'@'%' identified by 'root123';
drop user 'wupeiqi4'@'%';<ul>对于权限
all privileges除grant外的所有权限select 仅查权限select,insert 查和插入权限...usage 无访问权限alter 使用alter tablealter routine 使用alter procedure和drop procedurecreate 使用create tablecreate routine 使用create procedurecreate temporary tables 使用create temporary tablescreate user 使用create user、drop user、rename user和revokeall privilegescreate view 使用create viewdelete 使用deletedrop 使用drop tableexecute 使用call和存储过程file 使用select into outfile 和 load data infilegrant option 使用grant 和 revokeindex 使用indexinsert 使用insertlock tables 使用lock tableprocess 使用show full processlistselect 使用selectshow databases 使用show databasesshow view 使用show viewupdate 使用updatereload 使用flushshutdown 使用mysqladmin shutdown(关闭MySQL)super
来源:https://www.cnblogs.com/sbhglqy/p/18157301
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