简介：本文章是我基于B站上SQL播放量第一的MySQL 基础+高级篇- 数据库 -sql -尚硅谷视频所做的笔记，方便记录自己的学习过程。

说明：

1. 本文章是基于视频中老师讲课的案例、部分测试题。*
2. 所需的配套资料（来自B站评论区）。附一个链接：
   B站黎曼的猜想视频配套资料提取码: k6kq

案例讲解，基础查询

select * from employees;desc departments;select * from departments;select distinct job_id from employees;select concat(first_name,',',last_name,',',job_id,',',ifnull(commission_pct,0)) as out_put
from employees;select concat(first_name,',',last_name,',',job_id,',',ifnull(commission_pct,0)) as out_put
from employees;

案例讲解，条件查询

select salary from employees;select last_name,department_id,salary*12*(1+ifnull(commission_pct,0)) as 年薪
from employees;select last_name,salary
from employees
where salary > 12000;select last_name,salary
from employees
where salary < 5000 or salary > 12000;select last_name,department_id
from employees
where department_id = 20 or department_id = 50;select last_name,job_id
from employees
where manager_id is null;select last_name
from employees
where last_name like '%a%';

测试题1讲解

select salary,last_name
from employees
where commission_pct is null and salary < 18000;select * from employees
where job_id <> 'IT' or salary = 12000;desc departments;select location_id
from departments;select * from employees
where commission_pct like '%%' and last_name like '%%';select last_name,department_id,salary*12*(1+ifnull(commission_pct,0)) as 年薪
from employees
order by 年薪 desc,last_name;

排序查询

select last_name,salary
from employees
where salary < 8000 or salary > 17000
order by salary desc;select last_name,salary
from employees
where salary not between 8000 and 17000
order by salary desc;select email from employees;select * from employees
where email like '%e%'
order by length(email) desc, department_id asc;

单行函数

#显示系统时间日期+时间
select now();select employee_id,last_name,salary,salary*(1+0.2) as 'new salary'
from employees;select length(last_name) 长度,substr(last_name,1,1) 首字符, last_name
from employees
order by last_name;selectconcat(last_name,' ','earns',' ',round(salary,0),' ','monthly but wants',' ',round(salary*3,0)) as 'Dream Salary'
from employees;select job_id as job,
case job_id
when 'AD_PRES' then 'A'
when 'ST_MAN' then 'B'
when 'IT_PROG' then 'C'
when 'SA_PRE' then 'D'
when 'ST_CLERK' then 'E'
end as Grade
from employees
where job_id = 'AD_PRES';select last_name,job_id as Job_id,
case job_id
when 'AD_PRES' then 'A'
when 'ST_MAN' then 'B'
when 'IT_PROG' then 'C'
when 'SA_PRE' then 'D'
when 'ST_CLERK' then 'E'
end as Grade
from employees
where job_id = 'AD_PRES';select last_name,job_id as Job_id,
case job_id
when 'AD_PRES' then 'A'
when 'ST_MAN' then 'B'
when 'IT_PROG' then 'C'
when 'SA_PRE' then 'D'
when 'ST_CLERK' then 'E'
end as Grade
from employees
where job_id = 'AD_PRES';

查询相隔天数

select datediff(max(hiredate),min(hiredate)) as DIFFERENCE
from employees;

分组查询

select job_id,round(max(salary),2) max_sal,round(min(salary),2) min_sal,round((salary),2) avg_sal,round(sum(salary),2) sum_sal
from employees
group by job_id
order by job_id ASC;select max(salary)-min(salary) as DIFFERENCE
from employees;select manager_id,min(salary)
from employees
where manager_id is not null
group by manager_id
having min(salary) >= 6000;select job_id,count(*)
from employees
group by job_id;select department_id,count(*),avg(salary)
from employees
group by department_id
order by avg(salary) desc;

测试题2讲解

select round(max(salary),2),round(avg(salary),2)
from employees;select employee_id,job_id,last_name
from employees
order by department_id desc, salary asc;select * from employees
where job_id like '%a%e%';select trim('' from now());

作业讲解

select last_name,e.department_id,d.department_name
from employees e
left join departments d
on e.department_id = d.department_id;select job_id,location_id
from employees e join departments d
on e.department_id = d.department_id
where e.department_id = 90;select last_name,department_name,l.location_id,city
from departments d
join employees e
on d.department_id = e.department_id
join locations l
on d.location_id = l.location_id
where e.commission_pct is not null;select last_name,job_id,d.department_id,d.department_name
from departments d
join employees e
on d.department_id = e.department_id
join locations l
on d.location_id = l.location_id
where l.city = 'Toronto';select d.department_name,j.job_title,min(e.salary)
from departments d
join employees e
on d.department_id = e.department_id
join jobs j
on e.job_id = j.job_id
group by j.job_title,d.department_name;select l.country_id,count(*) 部门个数
from departments d
join employees e
on d.department_id = e.department_id
join locations l
on d.location_id = l.location_id
group by l.country_id
having count(e.department_id)> 2;select country_id,count(*) 部门个数
from departments d,locations l
where d.location_id = l.location_id
group by country_id
having count(*) > 2; select e.last_name employees,e.employee_id 'Emp#',m.last_name manager,m.employee_id 'Mgr#'
from employees e,employees m
where e.manager_id = m.employee_id
and e.last_name = 'Kochhar';

多表查询

select be.id,be.name,bo.*
from beauty be
left outer join boys bo
on be.boyfriend_id = bo.id
where be.id > 3;select city,d.*
from locations l
left join departments d
on d.location_id = l.location_id
where d.department_id is null;select city,d.*
from departments d
right join locations l
on l.location_id = d.location_id
where d.department_id is null;select * from departments;select e.*,d.department_name,d.department_id
from employees e
left join departments d
on e.department_id = d.department_id
where d.department_name = 'SAL' or d.department_name = 'IT';select e.*,d.department_name,d.department_id
from departments d
left join employees e
on e.department_id = d.department_id
where d.department_name = 'SAL' or d.department_name = 'IT';select job_id from employees
where employee_id = 141;select salary
from employees
where employee_id = 143;select last_name,job_id,salary
from employees
where job_id = (select job_id from employeeswhere employee_id = 141
)
and salary > (select salary
from employees
where employee_id = 143
);select last_name,job_id,salary
from employees
where salary = (select min(salary)from employees
);

#查询最低工资大于50号部门最低工资的部门id,及其最低工资
#1找50号部门最低工资
select min(salary) from employees
where department_id = 50;#2每一个部门最低工资
select department_id,min(salary)
from employees
group by department_id;#筛选2，且salary > 1
select department_id,min(salary)
from employees
group by department_id
having min(salary) > (select min(salary) from employeeswhere department_id = 50
);select department_id,min(salary)
from employees;select department_id,min(salary)
from employees
group by department_id;select department_id,min(salary)
from employees
group by department_id
having min(salary) > (select min(salary)from employeeswhere department_id = 50
);#1找141号员工的job_id
select job_id from employees
where employee_id = 141;#2找143号员工的salary
select salary from employees
where employee_id = 143;select last_name,job_id,salary
from employees
where job_id = (select job_id from employeeswhere employee_id = 141
)
and salary > (select salary from employeeswhere employee_id = 143
);

子查询

#子查询#找到Zlotkey所在的部门id
select department_id
from employees
where last_name = 'Zlotkey';#1
select employee_id,last_name,salary
from employees
where department_id = (select department_idfrom employeeswhere last_name = 'Zlotkey'
);#先找公司平均工资
select avg(salary)
from employees;#2
select employee_id,last_name,salary
from employees
where salary > (select avg(salary)from employees
);#各部门平均工资
select department_id,avg(salary)
from employees
group by department_id;#3查询各个部门中工资比本部门平均工资高的员工号，姓名和工资
select e.department_id,last_name,employee_id,salary
from employees e
inner join(select department_id,avg(salary) av_salfrom employeesgroup by department_id
) as av_dep
on e.department_id = av_dep.department_id
where salary > av_dep.av_sal;#4查询姓名中包含字母u的员工号
select department_id, employee_id,last_name
from employees
where last_name like '%u%';select e.employee_id,e.last_name
from employees e
inner join (select distinct department_id, employee_id,last_namefrom employeeswhere last_name like '%u%'
) as new_tab
on e.department_id = new_tab.department_id;select last_name,employee_id
from employees
where department_id in (select  distinct department_idfrom employeeswhere last_name like '%u%');#5先查询location_id=1700 所在部门
select department_id
from departments
where location_id = 1700;select employee_id
from employees e
where department_id in (select department_idfrom departmentswhere location_id = 1700
);
#6
select * from employees
where last_name = 'K_ing';select manager_id
from employees
where last_name = 'K_ing';select last_name,salary
from employees
where manager_id in (select manager_idfrom employeeswhere last_name = 'K_ing'
);#查询管理者是K_ing的员工姓名和工资
#1先找到姓名是K_ing的员工编号
#2再找manager_id=1 的员工姓名和工资
select employee_id
from employees
where last_name = 'K_ing';select last_name,salary
from employees
where manager_id in (select distinct employee_idfrom employeeswhere last_name = 'K_ing'
);#7查询工资最高的员工姓名，要求first_name和last_name显示为一列，列名为姓.名
#1先找到工资最高的员工编号
select employee_id
from employees
where salary >= (select max(salary) from employees);#2再employee_id in 1  （concat连接）
select concat(first_name,'.',last_name) 姓名
from employees
where employee_id = (select employee_idfrom employeeswhere salary >= (select max(salary) from employees)
);#简单方法(优化)
select concat(first_name,'.',last_name) 姓名
from employees
where salary = (select max(salary)from employees
);

测试题3讲解

#1查询所有学员的邮箱用户名（@前的字符） john@126.com
select substr(email,1,instr(email,'@')-1) 用户名
from stuinfo;#2查询男生和女生个数
select count(*) 个数，sex
from stuinfo
group by sex;#3查询年龄大于18所有学生姓名和年级名
select name,gradeName
from stuinfo
join grade
on stuinfo.gradeId = grade.id
where age > 18;#4查询那个年级学生最小年龄大于二十岁
#找到每个年级的最小年龄
select min(age)
from stuinfo
group by gradeId;#5查询语句执行的先后顺序
#select\from\join\on\where\group by\having\order by\limit
#from\join\on\where\group by\having\select\order by\limit

子查询经典案例讲解

#1
select last_name,salary
from employees
where salary = (select min(salary)from employees
);#2
#最低平均工资
select department_id
from employees
group by department_id
order by avg(salary)
limit 1;select d.*
from departments d
join (select department_id
from employees
group by department_id
order by avg(salary)
limit 1
) as new_tab
on d.department_id = new_tab.department_id;#3
#先找各部门平均工资
select avg(salary)
from employees
group by department_id
order by avg(salary)
limit 1;select d.*,ag
from departments d
join (select avg(salary) ag,department_idfrom employeesgroup by department_idorder by avg(salary)limit 1
) as ag_dep
on d.department_id = ag_dep.department_id;#4找出平均工资最高的job信息
#先找出平均工资最高的job_id
select avg(salary) as ag_sal,job_id
from employees
group by job_id
order by avg(salary) desc
limit 1;select j.*,ag_sal
from jobs j
join (select avg(salary) as ag_sal,job_idfrom employeesgroup by job_idorder by avg(salary) desclimit 1
) as new_tab
on j.job_id = new_tab.job_id;#5查询公司平均工资
select avg(salary) man_ag
from employees;#查询各部门的平均工资
select avg(salary) dep_ag,department_id
from employees
group by department_id;#用各部门>公司工资
select d.department_id,d.department_name,dep_ag
from departments d
join (select avg(salary) dep_ag,department_id
from employees
group by department_id) as new_tab
on d.department_id = new_tab.department_id
where dep_ag > (select avg(salary) man_ag
from employees);#6查询公司所有manager详细信息
select distinct manager_id
from employees;
select *
from employees
where employee_id in (select distinct manager_idfrom employees
);#7各个部门中，最高工资中最低的那个部门，最低工资是多少
#先查询各个部门中最高工资
select max(salary),department_id
from employees
group by department_id;#再找到以上最低的工资及其所在部门
select department_id
from employees
group by department_id
order by max(salary)
limit 1;#查询上述部门编号所对应信息
select min(salary),department_id
from employees
where department_id = (select department_idfrom employeesgroup by department_idorder by max(salary)limit 1
);#8查询平均工资最高的部门的manager的详细信息：last_name,department_id,email,salary
#先查出各部门平均工资中最高的
select department_id
from employees
group by department_id
order by avg(salary) desc
limit 1;#找到部门id是上述id,所对应的manager_id
select distinct manager_id
from employees
where department_id = (select department_idfrom employeesgroup by department_idorder by avg(salary) desclimit 1
);#根据上述manager_id得到employee_id,找到姓名，部门号，邮箱，薪资
select last_name,department_id,email,salary
from employees
where employee_id in (
select distinct manager_id
from employees
where department_id = (select department_idfrom employeesgroup by department_idorder by avg(salary) desclimit 1
)
);

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