-- 如果存在，删除名称hrs的数据库 drop database if exists `hrs`; -- 创建名为hrs指定默认字符集的数据库 create database `hrs` default charset utf8mb4; -- 切换到hrs数据库 use `hrs`; -- 创建部门表 create table `tb_dept` ( `dno` int not null comment '编号', `dname` varchar(10) not null comment '名称', `dloc` varchar(20) not null comment 所在地， primary key (`dno`) ); -- 插入4个部门 insert into `tb_dept` values (10, '会计部', 北京， (20, 研发部， 成都， (30, 销售部， 重庆， (40, 运维部， 深圳； -- 创建员工表 create table `tb_emp` ( `eno` int not null comment 员工编号， `ename` varchar(20) not null comment 员工姓名， `job` varchar(20) not null comment 员工职位， `mgr` int comment 主管编号， `sal` int not null comment 员工月薪， `comm` int comment 每月补贴， `dno` int not null comment 所在部门编号， primary key (`eno`), constraint `fk_emp_mgr` foreign key (`mgr`) references tb_emp (`eno`), constraint `fk_emp_dno` foreign key (`dno`) references tb_dept (`dno`) ); -- 插入14个员工 insert into `tb_emp` values (7800, 张三丰， '总裁', null, 9000, 1200, 20), (2056, '乔峰', 分析师， 7800, 5000, 1500, 20), (3088, 李莫愁， 设计师， 2056, 3500, 800, 20), (3211, 张无忌， 程序员， 2056, 3200, null, 20), (3233, 丘处机， 程序员， 2056, 3400, null, 20), (3251, 张翠山， 程序员， 2056, 4000, null, 20), (5566, 宋远桥， 会计师， 7800, 4000, 1000, 10), (5234, '郭靖', '出纳', 5566, 2000, null, 10), (3344, '黄蓉', 销售主管， 7800, 3000, 800, 30), (1359, 胡一刀， 销售员， 3344, 1800, 200, 30), (4466, 苗人凤， 销售员， 3344, 2500, null, 30), (3244, 欧阳锋， 程序员， 3088, 3200, null, 20), (3577, '杨过', '会计', 5566, 2200, null, 10), (3588, 朱九真， '会计', 5566, 2500, null, 10);
-- 面试可能需要3中以上的写法 -- 方法1：排序 limit（有bug，性能差，不推荐) select ename, sal from tb_emp order by sal desc limit 1; -- 方法2：嵌套查询 select ename, sal from tb_emp where sal = ( select max(sal) from tb_emp); -- 1. 关系运算：封闭 - 关系运算的结果仍然是关系 -- a. 投影（select） -- b. 别名（as） -- c. 选择（where） -- d. 交集（intersect）/ 并集（union）/ 差集（except） -- e. 连接（join） -- 2. 谓词 --> true / false / unknown -- in / not in -- exists / not exists -- is pull / is not pull -- all / any / some -- 方法3：all 谓词 select ename, sal from tb_emp where sal >= all(select sal from tb_emp); -- 查常量 select 'x' from tb_emp; select 'x' from dual; -- 方法4：exists 谓词 select ename, sal from tb_emp t1 where not exists (select 'x' from tb_emp t2 where t2.sal > t1.sal); -- 方法5:计数法(可推广到前几名) select ename, sal from tb_emp t1 where (select count(*) from tb_emp t2 where t2.sal > t1.sal) = 0; select concat('a', 'xxx') from dual;
-- 推荐用coalesce() select ename as 姓名, (sal coalesce(comm, 0))*13 as 年薪 from tb_emp order by 年薪 desc; select ename as 姓名, (sal ifnull(comm, 0))*13 as 年薪 from tb_emp;
select dno, count(*) from tb_emp group by dno;
select dname, count(eno) from tb_emp right outer join tb_dept on tb_emp.dno = tb_dept.dno group by tb_dept.dno; select dname, coalesce(total, 0) as total from tb_dept t1 left join (select dno, count(*) as total from tb_emp group by dno) t2 on t1.dno = t2.dno;
select ename, sal from tb_emp where sal > (select avg(sal) from tb_emp);
select ename, dno, sal from tb_emp natural join ( select dno, avg(sal) as avg_sal from tb_emp group by dno) t where sal > avg_sal; select ename, t1.dno, sal from tb_emp t1 inner join ( select dno, avg(sal) as avg_sal from tb_emp group by dno) t2 on t1.dno = t2.dno where sal > avg_sal;
select ename, dno, sal from tb_emp natural join tb_dept natural join ( select dno, max(sal) as max_sal from tb_emp group by dno) t
where sal = max_sal;
select ename,
sal,
dname
from tb_emp t1 inner join tb_dept t2
inner join ( select dno,
max(sal) as max_sal
from tb_emp
group by dno) t3
on t1.dno = t2.dno
and t2.dno = t3.dno
where sal = max_sal;
select ename,
job
from tb_emp t1
where exists (select 'x'
from tb_emp t2
where t1.eno = t2.mgr);
select ename,
job
from tb_emp
where eno in (select distinct mgr
from tb_emp
where mgr is not null);
select ename,
job
from tb_emp right join (select distinct mgr
from tb_emp
where mgr is not null) t
on tb_emp.eno = t.mgr;
-- MySQL 5.x
select *
from (select @x := @x + 1 as r,
ename,
sal
from tb_emp, (select @x := 0) t1
order by sal desc) t2
where r between 4 and 6;
-- MySQL 8.x
-- 窗口函数
-- row_number() - 对列排名
-- rank() - 排序 并列之后 按数量排
-- dense_rank() - 排序 并列之后 按排名排
select *
from (select ename,
sal,
row_number() over (order by sal desc) as r1,
rank() over (order by sal desc) as r2,
dense_rank() over (order by sal desc) as r3
from tb_emp) t
where r2 between 4 and 6;
-- MySQL 5.x
select ename,
sal,
dno
from tb_emp t1
where (select count(*)
from tb_emp t2
where t1.dno = t2.dno
and t2.sal > t1.sal) < 2
order by dno asc, sal desc;
-- MySQL 8.x
select ename,
sal,
dno
from (select ename,
sal,
dno,
rank() over (partition by dno order by sal desc) as r
from tb_emp) t
where r < 3;
-- grant（授予权限）/ revoke（召回权限）
-- 删除用户
drop user 'wangdachui'@'%';
-- 创建用户（访问账号）
create user 'wangdachui'@'%'identified by 'wang.618.888';
create user 'wangdachui'@'10.7.183.%' identified by 'Dachui.618';
-- 修改用户密码
alter user 'wangdachui'@'%' identified by 'Hello.world!123';
-- 授权
grant select on hrs.* to 'wangdachui'@'%';
grant insert, delete, update on hrs.* to 'wangdachui'@'%';
grant select on school.* to 'wangdachui'@'%';
grant create on *.* to 'wangdachui'@'%';
-- 授予所有权限
grant all privileges on *.* to 'wangdachui'@'%' with grant option;
-- 召回
revoke create on *.* from 'wangdachui'@'%';
revoke select on school.* from 'wangdachui'@'%';
-- 召回所有权限
revoke all privileges on *.* from 'wangdachui'@'%';