1.多列子查询
查询与141号或者174号员工的 manager_id和department_id相同的其他员工的employee_id,manager_id,department_id
//单列子查询的方式
select employee_id,department_id
from employees e1
wheremanager_id in (
select manager_id from employee where employee_id in(141,174);
)and department_id in (
select department_id from employee where employee_id in(141,174);
)
and employee_id not in (141,174);
select employee_id,department_id
from employees e1
where(manager_id,department_id) in (
select manager_id,department_idfrom employee where employee_id in(141,174);
)
and employee_id not in (141,174);
2.在from子列中使用子查询
返回比本部门平均工资高的员工的last_name,department_id,salary 及平均工资
select last_name,salary
from employees e1
where salary >(
select avg(salary)
from employees e2
where e1.department_id=e2.department_id
group by department_id
);
//使用from字句
select last_name,salary,avg_sal
from employees e1,(select department_id,avg(salary) as avg_sal from employees group by department_id ) e2
where e1.department_id=e2.department_id;
3.单列子查询
条件表达式 case
显示员工employee_id,last_name和location。其中，若员工department_id和location_id 为 1800的department_id相同，则显示Canada，否则USA
select employee_id,last_name,
(case department_idwhen(select department_id from departments where location_id=1800) then 'Canda' else 'USA'end ) location
from employees;
在order by中使用单列子查询
显示员工的employee_id,要求按照员工department_name 排序
select employee_id,last_name
from employees e1
order by (select department_name
from departments d
where e1.department_id =d.department_id);
4.相关子查询
定义：相关子查询按照一行接一行的顺序执行，主查询的每一行都执行一次子查询。
5.EXISTS 操作符
定义：如果子查询中满足条件行，则返回true，不满足条件返回false
查询公司管理者的employee_id,job_id,department_id信息
select employee_id,department_id
from empolyee_id e1
where exists ( //只需要告诉我能查到，不需要返回具体数据
select 'asddsa' from employees e2 where e1.employee_id=e2.manager_id
);
6.WITH子句
查询公司中工资比Able高的员工的信息
select employee_id,salary
from employees
where salary >(
select salary from employees where last_name='Abel'
);
//使用with子句实现
with Abel_salas (select salary from employees where last_name='Abel') //先查询able的工资，把Abel_sal理解为表
select employee_id,salary
from employees
where salary >(
select salary form Abel_sal
)
