子查询

# 子查询

select * from student where borndate > (

select borndate from student where stuname='崔今生'
);

/**
先进行"子查询"后进行"父查询"
**/

①先进行“子查询”

select * from student where studentno =(
select studentno from subject where studentresult =100 and subjectid=(
select subjectid from result where subjectname='JavaSE'
));

②进行“父查询”

select max(studentresult),min(studentresult) from result
where subjectid=(
select subjectid from subject where subjectname ='HTML和CSS课程'
) and examdate =(
select max(examdate) from result where subjectid =(
select subjectid from subject where subjectname ='HTML和CSS课程'
)
);

# in子查询

--查询"JavaSE"课程考试成绩不及格的学生名单

select stuname from student where studnetno in (
select studentno from result where studentresult<60 and subjectid=(
select subjectid from subject where subjectname = 'JavaSE'
) 
);

# where子查询

--查询员工编号最大的是谁？

select * from s_emp where id =(
select max(id) from s_emp
);

--查询最大的部门编号是谁？

select * from s_emp where dept_id =(
select max(dept_id) from s_emp
)

--查询公司所有的领导

select * from s_emp where id in (
select distinct manager_id from s_emp where mangager_id is not null
)

# having和from子查询

--查询部门中平均工资大于32号部门平均工资的部门信息（显示部门编号和平均工资）

select dept_id 部门编号,avg(salary)平均工资 from s_emp group by dept_id
having avg(salary)>(
select avg(salary) from s_emp where dept_id=32
)

--查询员工信息，条件为工资大于1400中，5号员工是谁？

select * from (
select * from s_emp where salary>1400 
) where id =5;

--小结：三个关键字支持子查询：where.../ having.../ from...