嵌套子查询subquery
单行子查询
select select_list
from table
where expr operator
(select select_list from table);
operator includes a comparison condition such as >, =, or IN
如：
select last_name,hire_date
from employees
where hire_date > (select hire_date from employees where last_name = 'Davies');
[可选] and ID=(select .......);
如:
select A from table
group by C
having min(column)>(select ......);
当子查询有group by 时，其输出行数只能是1行；
多行子查询
IN , ANY , ALL
select employee_id,last_name,job_id,salary
from employees
where salary<ANY
(select salary from employees where job_id='IT_PROG')
and job_id <> 'IT_PROG';
说明：
<ANY means less than the maximum. >ANY means more than the minimum. =ANY is equivalent to IN.
多列子查询
Syntax:
SELECT column, column, ...
FROM table
WHERE (column, column, ...) IN
(SELECT column, column, ...
FROM table
WHERE condition);
如：
select first_name,dapartment_id,salary
from employees
where (salary,department_id) IN
(select min(salary),department_id
from employees
group by department_id)
order by department_id;
空值子查询
子查询语句要把NULL处理掉才有结果
SELECT last_name FROM employees
WHERE employee_id NOT IN
(SELECT manager_id
FROM employees
WHERE manager_id IS NOT NULL);