-- select ename, sal from tb_emp order by sal desc limit 1;
select ename, sal from tb_emp where sal=(
select max(sal) from tb_emp
);
-- 查询员工的姓名和年薪((月薪+补贴)*12)
select ename, (sal+ifnull(comm, 0))*12 as 年薪 from tb_emp order by 年薪 desc;
-- 查询有员工的部门的编号和人数 - 分组查询+聚合函数
select dno, count(dno) from tb_emp group by dno with rollup;
-- 查询所有部门的名称和人数 - 子查询+连接查询（左外）
select dname as 部门名称, ifnull(total, 0) as 人数 from tb_dept t1 left join (select dno, count(dno) as total from tb_emp group by dno) t2 on t1.dno=t2.dno;
-- 查询月薪最高的员工(Boss除外)的姓名和工资 - 空值判断
select ename, sal from tb_emp where sal=(select max(sal) from tb_emp where mgr is not null);
-- 查询月薪超过平均薪水的员工的姓名和工资
select ename, sal from tb_emp where sal>(select avg(sal) as avgsal from tb_emp);
-- 查询月薪超过其所在部门平均薪水的员工的姓名、部门编号和工资
select ename, t1.dno, sal, round(avgsal, 2) from tb_emp t1 inner join (select dno, avg(sal) as avgsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal>avgsal;
-- 查询部门中薪水最高的人姓名、工资和所在部门名称
select ename, sal, dname from (select ename, sal, t1.dno from tb_emp t1 inner join (select dno, max(sal) as maxsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal=maxsal) t3 inner join tb_dept t4 on t3.dno=t4.dno;
-- 查询主管的姓名和职位
select ename, job from tb_emp where eno in (select distinct mgr from tb_emp where mgr is not null);
-- 通常不推荐使用in或者not in集合运算和distinct去重操作
-- 可以考虑用exists或not exists替代掉集合运算和去重操作
select ename, job from tb_emp t1 where exists (select 'x' from tb_emp t2 where t1.eno=t2.mgr);
-- 查询月薪排名4~6名的员工姓名和工资
select ename, sal from tb_emp order by sal desc limit 3, 3;
select ename, sal from tb_emp order by sal desc limit 3 offset 3;
-- explain生成执行计划
explain select eno, ename from tb_emp where eno=7800;
explain select eno, ename from tb_emp where eno<>7900;
explain select eno, ename from tb_emp where ename='张三丰';
explain select eno, ename from tb_emp where ename like '张%';
explain select eno, ename from tb_emp where ename like '%张';
explain select eno, ename from tb_emp where ename<>'张三丰';
-- 视图：查询的快照（简化查询操作）
-- 通过视图可以将用户的访问权限限制到某些指定的列上
create view vw_emp_dept as
select eno, ename, dname from tb_emp t1 inner join tb_dept t2 on t1.dno=t2.dno;
-- select ename, sal from tb_emp order by sal desc limit 1;
select ename, sal from tb_emp where sal=(
select max(sal) from tb_emp
);
-- 查询员工的姓名和年薪((月薪+补贴)*12)
select ename, (sal+ifnull(comm, 0))*12 as 年薪 from tb_emp order by 年薪 desc;
-- 查询有员工的部门的编号和人数 - 分组查询+聚合函数
select dno, count(dno) from tb_emp group by dno with rollup;
-- 查询所有部门的名称和人数 - 子查询+连接查询（左外）
select dname as 部门名称, ifnull(total, 0) as 人数 from tb_dept t1 left join (select dno, count(dno) as total from tb_emp group by dno) t2 on t1.dno=t2.dno;
-- 查询月薪最高的员工(Boss除外)的姓名和工资 - 空值判断
select ename, sal from tb_emp where sal=(select max(sal) from tb_emp where mgr is not null);
-- 查询月薪超过平均薪水的员工的姓名和工资
select ename, sal from tb_emp where sal>(select avg(sal) as avgsal from tb_emp);
-- 查询月薪超过其所在部门平均薪水的员工的姓名、部门编号和工资
select ename, t1.dno, sal, round(avgsal, 2) from tb_emp t1 inner join (select dno, avg(sal) as avgsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal>avgsal;
-- 查询部门中薪水最高的人姓名、工资和所在部门名称
select ename, sal, dname from (select ename, sal, t1.dno from tb_emp t1 inner join (select dno, max(sal) as maxsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal=maxsal) t3 inner join tb_dept t4 on t3.dno=t4.dno;
-- 查询主管的姓名和职位
select ename, job from tb_emp where eno in (select distinct mgr from tb_emp where mgr is not null);
-- 通常不推荐使用in或者not in集合运算和distinct去重操作
-- 可以考虑用exists或not exists替代掉集合运算和去重操作
select ename, job from tb_emp t1 where exists (select 'x' from tb_emp t2 where t1.eno=t2.mgr);
-- 查询月薪排名4~6名的员工姓名和工资
select ename, sal from tb_emp order by sal desc limit 3, 3;
select ename, sal from tb_emp order by sal desc limit 3 offset 3;
-- explain生成执行计划
explain select eno, ename from tb_emp where eno=7800;
explain select eno, ename from tb_emp where eno<>7900;
explain select eno, ename from tb_emp where ename='张三丰';
explain select eno, ename from tb_emp where ename like '张%';
explain select eno, ename from tb_emp where ename like '%张';
explain select eno, ename from tb_emp where ename<>'张三丰';
-- 视图：查询的快照（简化查询操作）
-- 通过视图可以将用户的访问权限限制到某些指定的列上
create view vw_emp_dept as
select eno, ename, dname from tb_emp t1 inner join tb_dept t2 on t1.dno=t2.dno;
select ename, dname from vw_emp_dept;
drop view vw_emp_dept;
-- 索引（index）
-- 索引可以加速查询所以应该在经常用于查询筛选条件的列上建立索引
-- 索引会使用额外的存储空间而且会让增删改变得更慢（因为要更新索引）
-- 所以不能够滥用索引
create index idx_emp_ename on tb_emp (ename);
drop index idx_emp_ename on tb_emp;
-- 创建存储过程
create procedure sp_dept_avg_sal(deptno int, out avgsal float)
begin
select avg(sal) into avgsal from tb_emp where dno=deptno;
end;
-- 调用存储过程
call sp_dept_avg_sal(20, @a);
-- 通过输出参数取出部门平均工资
select @a;
-- 删除存储过程
drop procedure sp_dept_avg_sal;
create trigger tr_dept_update
after update on tb_dept for each row
begin
update tb_emp set dno=new.dno where dno=old.dno;
end;
drop trigger tr_dept_update;
-- DCL：授予权限(grant to)和召回权限(revoke from)
create user 'hellokitty'@'%' identified by '123123';
grant all privileges on hrs.* to 'hellokitty'@'%';
revoke insert, delete, update on hrs.* from 'hellokitty'@'%';
drop user 'hellokitty'@'%';
-- 事务（transaction）- 把多个增删改的操作做成不可分割的原子性操作
-- 要么全部都做，要么全都不做
-- start transaction;
-- begin;
-- delete from tb_emp;
-- commit;
-- rollback;</string>
<string>-- 事务（transaction）- 把多个增删改的操作做成不可分割的原子性操作
-- 要么全部都做，要么全都不做
-- start transaction;
-- begin;
-- delete from tb_emp;
-- commit;
-- rollback;</string>
<string>delete from tb_emp</string>
<string>alter table tb_emp drop foreign key fk_emp_mgr</string>
-- select ename, sal from tb_emp order by sal desc limit 1;
select ename, sal from tb_emp where sal=(
select max(sal) from tb_emp
);
-- 查询员工的姓名和年薪((月薪+补贴)*12)
select ename, (sal+ifnull(comm, 0))*12 as 年薪 from tb_emp order by 年薪 desc;
-- 查询有员工的部门的编号和人数 - 分组查询+聚合函数
select dno, count(dno) from tb_emp group by dno with rollup;
-- 查询所有部门的名称和人数 - 子查询+连接查询（左外）
select dname as 部门名称, ifnull(total, 0) as 人数 from tb_dept t1 left join (select dno, count(dno) as total from tb_emp group by dno) t2 on t1.dno=t2.dno;
-- 查询月薪最高的员工(Boss除外)的姓名和工资 - 空值判断
select ename, sal from tb_emp where sal=(select max(sal) from tb_emp where mgr is not null);
-- 查询月薪超过平均薪水的员工的姓名和工资
select ename, sal from tb_emp where sal>(select avg(sal) as avgsal from tb_emp);
-- 查询月薪超过其所在部门平均薪水的员工的姓名、部门编号和工资
select ename, t1.dno, sal, round(avgsal, 2) from tb_emp t1 inner join (select dno, avg(sal) as avgsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal>avgsal;
-- 查询部门中薪水最高的人姓名、工资和所在部门名称
select ename, sal, dname from (select ename, sal, t1.dno from tb_emp t1 inner join (select dno, max(sal) as maxsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal=maxsal) t3 inner join tb_dept t4 on t3.dno=t4.dno;
-- 查询主管的姓名和职位
select ename, job from tb_emp where eno in (select distinct mgr from tb_emp where mgr is not null);
-- 通常不推荐使用in或者not in集合运算和distinct去重操作
-- 可以考虑用exists或not exists替代掉集合运算和去重操作
select ename, job from tb_emp t1 where exists (select 'x' from tb_emp t2 where t1.eno=t2.mgr);
-- 查询月薪排名4~6名的员工姓名和工资
select ename, sal from tb_emp order by sal desc limit 3, 3;
select ename, sal from tb_emp order by sal desc limit 3 offset 3;
-- explain生成执行计划
explain select eno, ename from tb_emp where eno=7800;
explain select eno, ename from tb_emp where eno<>7900;
explain select eno, ename from tb_emp where ename='张三丰';
explain select eno, ename from tb_emp where ename like '张%';
explain select eno, ename from tb_emp where ename like '%张';
explain select eno, ename from tb_emp where ename<>'张三丰';
-- 视图：查询的快照（简化查询操作）
-- 通过视图可以将用户的访问权限限制到某些指定的列上
create view vw_emp_dept as
select eno, ename, dname from tb_emp t1 inner join tb_dept t2 on t1.dno=t2.dno;
select ename, dname from vw_emp_dept;
drop view vw_emp_dept;
-- 索引（index）
-- 索引可以加速查询所以应该在经常用于查询筛选条件的列上建立索引
-- 索引会使用额外的存储空间而且会让增删改变得更慢（因为要更新索引）
-- 所以不能够滥用索引
create index idx_emp_ename on tb_emp (ename);
drop index idx_emp_ename on tb_emp;
-- 创建存储过程
create procedure sp_dept_avg_sal(deptno int, out avgsal float)
begin
select avg(sal) into avgsal from tb_emp where dno=deptno;
end;
-- 调用存储过程
call sp_dept_avg_sal(20, @a);
-- 通过输出参数取出部门平均工资
select @a;
-- 删除存储过程
drop procedure sp_dept_avg_sal;
create trigger tr_dept_update
after update on tb_dept for each row
begin
update tb_emp set dno=new.dno where dno=old.dno;
end;
drop trigger tr_dept_update;
-- DCL：授予权限(grant to)和召回权限(revoke from)
create user 'hellokitty'@'%' identified by '123123';
grant all privileges on hrs.* to 'hellokitty'@'%';
revoke insert, delete, update on hrs.* from 'hellokitty'@'%';
-- select ename, sal from tb_emp order by sal desc limit 1;
select ename, sal from tb_emp where sal=(
select max(sal) from tb_emp
);
-- 查询员工的姓名和年薪((月薪+补贴)*12)
select ename, (sal+ifnull(comm, 0))*12 as 年薪 from tb_emp order by 年薪 desc;
-- 查询有员工的部门的编号和人数 - 分组查询+聚合函数
select dno, count(dno) from tb_emp group by dno with rollup;
-- 查询所有部门的名称和人数 - 子查询+连接查询（左外）
select dname as 部门名称, ifnull(total, 0) as 人数 from tb_dept t1 left join (select dno, count(dno) as total from tb_emp group by dno) t2 on t1.dno=t2.dno;
-- 查询月薪最高的员工(Boss除外)的姓名和工资 - 空值判断
select ename, sal from tb_emp where sal=(select max(sal) from tb_emp where mgr is not null);
-- 查询月薪超过平均薪水的员工的姓名和工资
select ename, sal from tb_emp where sal>(select avg(sal) as avgsal from tb_emp);
-- 查询月薪超过其所在部门平均薪水的员工的姓名、部门编号和工资
select ename, t1.dno, sal, round(avgsal, 2) from tb_emp t1 inner join (select dno, avg(sal) as avgsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal>avgsal;
-- 查询部门中薪水最高的人姓名、工资和所在部门名称
select ename, sal, dname from (select ename, sal, t1.dno from tb_emp t1 inner join (select dno, max(sal) as maxsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal=maxsal) t3 inner join tb_dept t4 on t3.dno=t4.dno;
-- 查询主管的姓名和职位
select ename, job from tb_emp where eno in (select distinct mgr from tb_emp where mgr is not null);
-- 通常不推荐使用in或者not in集合运算和distinct去重操作
-- 可以考虑用exists或not exists替代掉集合运算和去重操作
select ename, job from tb_emp t1 where exists (select 'x' from tb_emp t2 where t1.eno=t2.mgr);
-- 查询月薪排名4~6名的员工姓名和工资
select ename, sal from tb_emp order by sal desc limit 3, 3;
select ename, sal from tb_emp order by sal desc limit 3 offset 3;
-- explain生成执行计划
explain select eno, ename from tb_emp where eno=7800;
explain select eno, ename from tb_emp where eno<>7900;
explain select eno, ename from tb_emp where ename='张三丰';
explain select eno, ename from tb_emp where ename like '张%';
explain select eno, ename from tb_emp where ename like '%张';
explain select eno, ename from tb_emp where ename<>'张三丰';
-- 视图：查询的快照（简化查询操作）
-- 通过视图可以将用户的访问权限限制到某些指定的列上
create view vw_emp_dept as
select eno, ename, dname from tb_emp t1 inner join tb_dept t2 on t1.dno=t2.dno;
select ename, dname from vw_emp_dept;
drop view vw_emp_dept;
-- 索引（index）
-- 索引可以加速查询所以应该在经常用于查询筛选条件的列上建立索引
-- 索引会使用额外的存储空间而且会让增删改变得更慢（因为要更新索引）
-- 所以不能够滥用索引
create index idx_emp_ename on tb_emp (ename);
drop index idx_emp_ename on tb_emp;
-- 创建存储过程
create procedure sp_dept_avg_sal(deptno int, out avgsal float)
begin
select avg(sal) into avgsal from tb_emp where dno=deptno;
end;
-- 调用存储过程
call sp_dept_avg_sal(20, @a);
-- 通过输出参数取出部门平均工资
select @a;
-- 删除存储过程
drop procedure sp_dept_avg_sal;
create trigger tr_dept_update
after update on tb_dept for each row
begin
update tb_emp set dno=new.dno where dno=old.dno;
end;
drop trigger tr_dept_update;
-- DCL：授予权限(grant to)和召回权限(revoke from)
create user 'hellokitty'@'%' identified by '123123'</string>
-- select ename, sal from tb_emp order by sal desc limit 1;
select ename, sal from tb_emp where sal=(
select max(sal) from tb_emp
);
-- 查询员工的姓名和年薪((月薪+补贴)*12)
select ename, (sal+ifnull(comm, 0))*12 as 年薪 from tb_emp order by 年薪 desc;
-- 查询有员工的部门的编号和人数 - 分组查询+聚合函数
select dno, count(dno) from tb_emp group by dno with rollup;
-- 查询所有部门的名称和人数 - 子查询+连接查询（左外）
select dname as 部门名称, ifnull(total, 0) as 人数 from tb_dept t1 left join (select dno, count(dno) as total from tb_emp group by dno) t2 on t1.dno=t2.dno;
-- 查询月薪最高的员工(Boss除外)的姓名和工资 - 空值判断
select ename, sal from tb_emp where sal=(select max(sal) from tb_emp where mgr is not null);
-- 查询月薪超过平均薪水的员工的姓名和工资
select ename, sal from tb_emp where sal>(select avg(sal) as avgsal from tb_emp);
-- 查询月薪超过其所在部门平均薪水的员工的姓名、部门编号和工资
select ename, t1.dno, sal, round(avgsal, 2) from tb_emp t1 inner join (select dno, avg(sal) as avgsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal>avgsal;
-- 查询部门中薪水最高的人姓名、工资和所在部门名称
select ename, sal, dname from (select ename, sal, t1.dno from tb_emp t1 inner join (select dno, max(sal) as maxsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal=maxsal) t3 inner join tb_dept t4 on t3.dno=t4.dno;
-- 查询主管的姓名和职位
select ename, job from tb_emp where eno in (select distinct mgr from tb_emp where mgr is not null);
-- 通常不推荐使用in或者not in集合运算和distinct去重操作
-- 可以考虑用exists或not exists替代掉集合运算和去重操作
select ename, job from tb_emp t1 where exists (select 'x' from tb_emp t2 where t1.eno=t2.mgr);
-- 查询月薪排名4~6名的员工姓名和工资
select ename, sal from tb_emp order by sal desc limit 3, 3;
select ename, sal from tb_emp order by sal desc limit 3 offset 3;
-- explain生成执行计划
explain select eno, ename from tb_emp where eno=7800;
explain select eno, ename from tb_emp where eno<>7900;
explain select eno, ename from tb_emp where ename='张三丰';
explain select eno, ename from tb_emp where ename like '张%';
explain select eno, ename from tb_emp where ename like '%张';
explain select eno, ename from tb_emp where ename<>'张三丰';
-- 视图：查询的快照（简化查询操作）
-- 通过视图可以将用户的访问权限限制到某些指定的列上
create view vw_emp_dept as
select eno, ename, dname from tb_emp t1 inner join tb_dept t2 on t1.dno=t2.dno;
select ename, dname from vw_emp_dept;
drop view vw_emp_dept;
-- 索引（index）
-- 索引可以加速查询所以应该在经常用于查询筛选条件的列上建立索引
-- 索引会使用额外的存储空间而且会让增删改变得更慢（因为要更新索引）
-- 所以不能够滥用索引
create index idx_emp_ename on tb_emp (ename);
drop index idx_emp_ename on tb_emp;
-- 创建存储过程
create procedure sp_dept_avg_sal(deptno int, out avgsal float)
begin
select avg(sal) into avgsal from tb_emp where dno=deptno;
alter table tb_score add constraint uni_score_stuid_couid unique (stuid, couid);
-- 插入学院数据
insert into tb_college (collname, collmaster, collweb) values
('计算机学院', '左冷禅', 'http://www.abc.com'),
('外国语学院', '岳不群', 'http://www.xyz.com'),
('经济管理学院', '风清扬', 'http://www.foo.com');
-- 插入学生数据
insert into tb_student (stuid, stuname, stusex, stubirth, stuaddr, collid) values
(1001, '杨逍', 1, '1990-3-4', '四川成都', 1),
(1002, '任我行', 1, '1992-2-2', '湖南长沙', 1),
(1033, '王语嫣', 0, '1989-12-3', '四川成都', 1),
(1572, '岳不群', 1, '1993-7-19', '陕西咸阳', 1),
(1378, '纪嫣然', 0, '1995-8-12', '四川绵阳', 1),
(1954, '林平之', 1, '1994-9-20', '福建莆田', 1),
(2035, '东方不败', 1, '1988-6-30', null, 2),
(3011, '林震南', 1, '1985-12-12', '福建莆田', 3),
(3755, '项少龙', 1, '1993-1-25', null, 3),
(3923, '杨不悔', 0, '1985-4-17', '四川成都', 3);
-- 插入老师数据
insert into tb_teacher (teaid, teaname, teatitle, collid) values
(1122, '张三丰', '教授', 1),
(1133, '宋远桥', '副教授', 1),
(1144, '杨逍', '副教授', 1),
(2255, '范遥', '副教授', 2),
(3366, '韦一笑', '讲师', 3);
-- 插入课程数据
insert into tb_course (couid, couname, coucredit, teaid) values
(1111, 'Python程序设计', 3, 1122),
(2222, 'Web前端开发', 2, 1122),
(3333, '操作系统', 4, 1122),
(4444, '计算机网络', 2, 1133),
(5555, '编译原理', 4, 1144),
(6666, '算法和数据结构', 3, 1144),
(7777, '经贸法语', 3, 2255),
(8888, '成本会计', 2, 3366),
(9999, '审计学', 3, 3366);
-- 插入选课数据
insert into tb_score (stuid, couid, scdate, scmark) values
(1001, 1111, '2017-09-01', 95),
(1001, 2222, '2017-09-01', 87.5),
(1001, 3333, '2017-09-01', 100),
(1001, 4444, '2018-09-03', null),
(1001, 6666, '2017-09-02', 100),
(1002, 1111, '2017-09-03', 65),
(1002, 5555, '2017-09-01', 42),
(1033, 1111, '2017-09-03', 92.5),
(1033, 4444, '2017-09-01', 78),
(1033, 5555, '2017-09-01', 82.5),
(1572, 1111, '2017-09-02', 78),
(1378, 1111, '2017-09-05', 82),
(1378, 7777, '2017-09-02', 65.5),
(2035, 7777, '2018-09-03', 88),
(2035, 9999, curdate(), null),
(3755, 1111, date(now()), null),
(3755, 8888, date(now()), null),
(3755, 9999, '2017-09-01', 92);
-- 查询所有学生信息
select * from tb_student;
-- 查询所有课程名称及学分(投影和别名)
select couname, coucredit from tb_course;
select couname as 课程名称, coucredit as 学分 from tb_course;
select stuname as 姓名, case stusex when 1 then '男' else '女' end as 性别 from tb_student;
select stuname as 姓名, if(stusex, '男', '女') as 性别 from tb_student;
-- 查询所有女学生的姓名和出生日期(筛选)
select stuname, stubirth from tb_student where stusex=0;
-- 查询所有80后学生的姓名、性别和出生日期(筛选)
select stuname, stusex, stubirth from tb_student where stubirth>='1980-1-1' and stubirth<='1989-12-31';
select stuname, stusex, stubirth from tb_student where stubirth between '1980-1-1' and '1989-12-31';
-- 查询姓"杨"的学生姓名和性别(模糊)
select stuname, stusex from tb_student where stuname like '杨%';
-- 查询姓"杨"名字两个字的学生姓名和性别(模糊)
select stuname, stusex from tb_student where stuname like '杨_';
-- 查询姓"杨"名字三个字的学生姓名和性别(模糊)
select stuname, stusex from tb_student where stuname like '杨__';
-- 查询名字中有"不"字或"嫣"字的学生的姓名(模糊)
select stuname, stusex from tb_student where stuname like '%不%' or stuname like '%嫣%';
-- 查询没有录入家庭住址的学生姓名(空值)
select stuname from tb_student where stuaddr is null;
-- 查询录入了家庭住址的学生姓名(空值)
select stuname from tb_student where stuaddr is not null;
-- 查询学生选课的所有日期(去重)
select distinct scdate from tb_score;
-- 查询学生的家庭住址(去重)
select distinct stuaddr from tb_student where stuaddr is not null;
-- 查询男学生的姓名和生日按年龄从大到小排列(排序)
-- asc - ascending - 升序（从小到大）
-- desc - descending - 降序（从大到小）
select stuname as 姓名, year(now())-year(stubirth) as 年龄 from tb_student where stusex=1 order by 年龄 desc;
-- 聚合函数：max / min / count / sum / avg
-- 查询年龄最大的学生的出生日期(聚合函数)
select min(stubirth) from tb_student;
-- 查询年龄最小的学生的出生日期(聚合函数)
select max(stubirth) from tb_student;
-- 查询男女学生的人数(分组和聚合函数)
select count(stuid) from tb_student;
select stusex, count(*) from tb_student group by stusex;
select stusex, min(stubirth) from tb_student group by stusex;
-- 查询课程编号为1111的课程的平均成绩(筛选和聚合函数)
select avg(scmark) from tb_score where couid=1111;
select min(scmark) from tb_score where couid=1111;
select count(scid) from tb_score where couid=1111;
select count(scmark) from tb_score where couid=1111;
-- 查询学号为1001的学生所有课程的平均分(筛选和聚合函数)
select avg(scmark) from tb_score where stuid=1001;
-- 查询每个学生的学号和平均成绩(分组和聚合函数)
select stuid as 学号, avg(scmark) as 平均分 from tb_score group by stuid;
-- 查询平均成绩大于等于90分的学生的学号和平均成绩
-- 分组以前的筛选使用where子句
-- 分组以后的筛选使用having子句
select stuid as 学号, avg(scmark) as 平均分 from tb_score group by stuid having 平均分>=90;
-- 查询年龄最大的学生的姓名(子查询/嵌套的查询)
select stuname from tb_student where stubirth=(
select min(stubirth) from tb_student
);
-- 查询年龄最大的学生姓名和年龄(子查询+运算)
select stuname as 姓名, year(now())-year(stubirth) as 年龄 from tb_student where stubirth=(
select min(stubirth) from tb_student
);
-- 查询选了两门以上的课程的学生姓名(子查询/分组条件/集合运算)
select stuname from tb_student where stuid=(
select stuid from tb_score group by stuid having count(stuid)>2
)
-- 查询学生姓名、课程名称以及成绩(连接查询)
select stuname, couname, scmark from tb_student t1, tb_course t2, tb_score t3 where t1.stuid=t3.stuid and t2.couid=t3.couid and scmark is not null;
select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null order by scmark desc limit 5 offset 10;
select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null order by scmark desc limit 10, 5;
-- 单表：65535TB
-- 单列：4G - LONGBLOB (Binary Large OBject) / LONGTEXT
-- 查询选课学生的姓名和平均成绩(子查询和连接查询)
select stuname, avgmark from tb_student t1, (select stuid, avg(scmark) as avgmark from tb_score group by stuid) t2 where t1.stuid=t2.stuid;
select stuname, avgmark from tb_student t1 inner join
(select stuid, avg(scmark) as avgmark from tb_score group by stuid) t2 on t1.stuid=t2.stuid;
-- 内连接（inner join）：只有满足连接条件的记录才会被查出来
-- 外连接（outer join）：左外连接 / 右外连接 / 全外连接
-- left outer join / right outer join / full outer join
-- 查询每个学生的姓名和选课数量(左外连接和子查询)
select stuname, ifnull(total, 0) from tb_student t1 left outer join (select stuid, count(stuid) as total from tb_score group by stuid) t2 on t1.stuid=t2.stuid;
</string>
<key>table</key>
<string>tb_score</string>
<key>view</key>
<string>SP_VIEW_CUSTOMQUERY</string>
<key>windowVerticalDividerPosition</key>
<real>163</real>
</dict>
</dict>
<key>encrypted</key>
<false/>
<key>format</key>
<string>connection</string>
<key>queryFavorites</key>
<array/>
<key>queryHistory</key>
<array>
<string>select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null order by scmark desc limit 5 offset 10</string>
<string>select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null order by scmark desc limit 10, 5</string>
<string>select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null order by scmark desc limit 5, 5</string>
<string>select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null order by scmark desc limit 50, 5</string>
<string>select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null order by scmark desc limit 5 offset 5</string>
<string>select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null order by scmark desc limit 5</string>
<string>select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null order by scmark desc</string>
<string>select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid where scmark is not null</string>
<string>select stuname, couname, scmark from tb_student t1, tb_course t2, tb_score t3 where t1.stuid=t3.stuid and t2.couid=t3.couid and scmark is not null</string>
<string>select stuname, couname, scmark from tb_student t1, tb_course t2, tb_score t3 where t1.stuid=t3.stuid and t2.couid=t3.couid where scmark is not null</string>
<string>-- 查询学生姓名、课程名称以及成绩(连接查询)
select stuname, couname, scmark from tb_student t1, tb_course t2, tb_score t3 where t1.stuid=t3.stuid and t2.couid=t3.couid where scmark is not null</string>
<string>select stuname, avgmark from tb_student t1 inner join
(select stuid, avg(scmark) as avgmark from tb_score group by stuid) t2 on t1.stuid=t2.stuid</string>
<string>select stuname, avgmark from tb_student t1, (select stuid, avg(scmark) as avgmark from tb_score group by stuid) t2 where t1.stuid=t2.stuid</string>
<string>select stuname, ifnull(total, 0) from tb_student t1 left outer join (select stuid, count(stuid) as total from tb_score group by stuid) t2 on t1.stuid=t2.stuid</string>
<string>select stuname, ifnull(total,0) from tb_student t1 left outer join (select stuid, count(stuid) as total from tb_score group by stuid) t2 on t1.stuid=t2.stuid</string>
<string>-- 查询选了两门以上的课程的学生姓名(子查询/分组条件/集合运算)
select stuname from tb_student where stuid=(
select stuid from tb_score group by stuid having count(stuid)>2
)
-- 查询学生姓名、课程名称以及成绩(连接查询)
-- 查询选课学生的姓名和平均成绩(子查询和连接查询)
-- 外连接（outer join）：左外连接 / 右外连接 / 全外连接
-- 查询每个学生的姓名和选课数量(左外连接和子查询)
select stuname, ifnull(total, 0) from tb_student t1 left outer join (select stuid, count(stuid) as total from tb_score group by stuid) t2 on t1.stuid=t2.stuid</string>
<string>select stuname, total from tb_student t1 left outer join
(select stuid, count(stuid) as total from tb_score group by stuid) t2 on t1.stuid=t2.stuid</string>
<string>select stuname, total from tb_student t1 inner join
(select stuid, count(stuid) as total from tb_score group by stuid) t2 on t1.stuid=t2.stuid</string>
<string>select stuid, count(stuid) from tb_score group by stuid</string>
<string>select stuname, couname, scmark from tb_student t1 inner join tb_score t3 on t1.stuid=t3.stuid inner join tb_course t2 on t2.couid=t3.couid</string>
> 1970年，IBM的研究员E.F.Codd在*Communication of the ACM*上发表了名为*A Relational Model of Data for Large Shared Data Banks*的论文，提出了关系模型的概念，奠定了关系模型的理论基础。后来Codd又陆续发表多篇文章，论述了范式理论和衡量关系系统的12条标准，用数学理论奠定了关系数据库的基础。
