oracle_day 4子查询

第一种方式

1.查询工资比Smith 工资高的员工信息

（1）查询Smith的工资

select salary

from s_emp

where last_name = 'Smith';

（2）比较

select *

from s_emp

where salary >940;

（3）合并

select*

from s_emp

where  salary >(

      select salary

      from s_emp

      where last_name = 'Smith'

      );

2.查询与Ngao所在部门是同一个部门的员工

（1）查询Ngao所在的部门

select dept_id

 from s_emp

where last_name = 'Ngao';

（2）查询部门为41的员工

select last_name

from s_emp

where dept_id =41;

（3）合并

select last_name

from s_emp

where dept_id =(

                   select dept_id

                   from s_emp

                   where last_name = 'Ngao'

      );

第二种方式

1. 查询员工信息，这些员工比自己所在部门平均工资要高

（1）求所有部门的平均工资

select dept_id,avg(salary)

from s_emp

group by dept_id；

（2）求员工的的工资比自己所在部门的平均工资高的

select emp.last_name,emp.salary,ss.dept_id,ss.sa

from s_emp

emp,(select dept_id,avg(salary) sa

                   from s_emp

                   group by dept_id)  ss

where emp.dept_id = ss.dept_id;

2. 求满足条件的员工所在部门的平均工资

select dept_id,avg(salary)

from s_emp

group by dept_id;

合并

select sa.last_name,sa.salary

from (select dept_id,avg(salary)

  from s_emp

  group by dept_id)  ss,(  select  *

  from s_emp

  where dept_id in(

    select  dept_id

    from s_emp

    group by dept_id

    having avg(salary) > (

      select avg(salary)

      from s_emp

      where dept_id = 41

    )

  )) sa

where sa.dept_id =ss.dept_id;