子查询：先执行内部再外部

Select last_name,salary,dept_id

From s_emp

Where dept_id in (

Select dept_id

From s_emp

Where dept_id is not null

);

 

Select last_name,dept_id

From s_emp

Where dept_id = (

Select dept_id

From s_emp

Where last_name=’Smith’

);

 

Select salary,last_name

From s_emp

Where salary<(

Select avg(salary)

From s_emp

);

 

Select last_name,dept_id,title

From s_emp

Where dept_id =(

Select dept_id

From s_emp

Where last_name=’Smith’

) and tltle = (select tltle

From s_emp

Where last_name=’Smith’

);

 

Select rownum,last_name,salary

From s_emp

Where rownum<=20

minus

Select rownum,last_name,salary

From s_emp

Where rownum<=10

;