MySQL---表的查询实战OJ

–查询工资高于500或岗位为MANAGER的雇员，同时还要满足他们的姓名首字母为大写的J

select * from emp where (sal>100 or job='manager') and ENAME LIKE 'j%';

–按照部门号升序而雇员的工资降序排序

SELECT ename,deptno ,sal from emp order by deptno asc , sal desc;

–使用年薪进行排序

select sal*12 as annual_salary from emp desc;

–显示工资最高的员工的名字和工作岗位

select ename,job,max(sal) from emp;

–显示工资高于平均工资的员工信息

select * from emp where sal > (select avg(sal) from emp);

–显示每个部门的平均工资和最高工资

select deptno,avg(sal),max(sal) from emp group by deptno;

–显示平均工资低于2000的部门号和和它的平均工资

select deptno,avg(sal) from emp group by deptno having avg(sal)<2000;

–显示每种岗位的雇员总数，平均工资

select count(*),avg(sal) from emp group by deptno;

–要emp表中的deptno = dept表中的deptno字段的记录

select emp.deptno,dept.deptno from emp,dept where emp.deptno=dept.deptno;

–显示部门号为10的部门名，员工名和工资

select dname,sal,ename from emp,dept where emp.deptno=dept.deptno and emp.deptno=10;

–显示各个员工的姓名，工资，及工资级别

select ename,sal,grade from emp,salgrade where emp.sal between salgrade.losal and salgrade.hisal;

–列出部门名称和这些部门的员工信息，同时列出没有员工的部门

select dept.dname,emp.*
from dept left join emp on
dept.deptno=emp.deptno;

–实战OJ6
–牛客：批量插入数据

insert into actor (actor_id,first_name,last_name,last_update) 
values(1,'PENELOPE','GUINESS',datetime('2006-02-15 12:34:33')),(2,'NICK','WAHLBERG',datetime('2006-02-15 12:34:33'));

–牛客：找出所有员工当前(to_date=‘9999-01-01’)具体的薪水salary情况，对于相同的薪水只显示一次,并按照逆序显示

select distinct salary from salaries where to_date 
like '9999-01-01' order by salary desc;

–牛客：查找晚入职员工的所有信息

select emp_no,birth_date,first_name,last_name,gender,hire_date 
from employees 
order by hire_date desc
 limit 1 offset 0;

–牛客：查找入职员工时间排名倒数第三的员工所有信息

select * from employees order by hire_date desc limit 1 offset 2;

–牛客：查找薪水涨幅超过15次的员工号emp_no以及其对应的涨幅次数t

select emp_no,count(salary) as t from salaries group by emp_no 
having count(salary)>15;

–牛客：获取所有部门当前manager的当前薪水情况，给出dept_no, emp_no以及salary，当前表示 to_date=‘9999-01-01’

select dept_no,dept_manager.emp_no,salary 
from dept_manager,salaries
where dept_manager.emp_no=salaries.emp_no 
and salaries.to_date like '9999-01-01'
and
dept_manager.to_date like '9999-01-01'
;

–牛客：从titles表获取按照title进行分组,每组个数大于等于2，给出title以及对应的数目t

select title,count(title) as t 
from titles group by title having count(title)>=2
;

–leetcode: duplicate-emails leetcode: big-countries

select  Email from Person
group by Email having count(Email)>1;

–leetcode: nth-highest-salary

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  RETURN (
      # Write your MySQL query statement below.
      select Salary from Employee order by salary desc limit 1 offset n-1
  );
END

–leetcode: big-countries

select name,population,area from  World
where population>25000000 or area> 3000000;

–牛客：查找字符串’10,A,B’ 中逗号’,'出现的次数cnt

select (length('10,A,B')-length(replace('10,A,B',',','')))/length(',') as cnt;

实战OJ8
–查找所有员工入职时候的薪水情况，给出emp_no以及salary，并按照emp_no进行逆序

select employees.emp_no,salary
from employees,salaries 
where (employees.emp_no=salaries.emp_no and employees.hire_date=salaries.from_date)
order by employees.emp_no desc;

–内连接

select ename,dname from emp inner join dept on dept.deptno=emp.deptno and ename='smith';

–外连接查询所有学生的成绩，如果这个学生没有成绩，也要将学生的个人信息显示出来

create table stu(id int,name varchar(20));
insert into stu values(1,'maia'),(2,'peter'),(3,'nancy');
create table exam (id int,grade int);
insert into exam values(1,56),(2,34),(3,68);

–对stu表和exam表联合查询，把所有的成绩都显示出来，即使这个成绩没有学生与它对应，也要显示出来

select * from stu right join exam on stu.id=exam.id;

–创建主键索引‘

create table user1(id int primary key,name varchar(10));
insert into user1 values(1,'jack'),(2,'tully');

–创建唯一键索引

create table user4(id int unique,name varchar(20));

MySQL---表的查询实战OJ

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