【Oracle】第六单元 子查询

单行比较示例

谁的薪水比Abel高

SELECT last_name
  FROM employees
 WHERE salary > (SELECT salary FROM employees WHERE last_name = 'Abel');

注：

单行比较必须对应单行子查询(返回单一结果值的查询)；比如= ， >

多行比较必须对应多行子查询(返回一个数据集合的查询)；比如 IN , > ANY, > ALL 等

谁的薪水最低

select employee_id, last_name
  from employees
 where salary = (select min(salary) from employees)

多行比较

小于任何一个IT部门人员薪水的人员

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';

注：<ANY 小于集合里任何一个值

小于所有IT部门人员薪水的人员

SELECT employee_id
      ,last_name
      ,job_id
      ,salary
  FROM employees
 WHERE salary < ALL (SELECT salary FROM employees WHERE job_id = 'IT_PROG')
   AND job_id <> 'IT_PROG';

注：<ALL 小于集合里所有的值