题解 | #使用含有关键字exists查找未分配具体部门的员工的所有信息。#

mysql not exists的语法,对比两种用法的差别

用exitst

select * from employees e
where not exists 
(select emp_no from dept_emp d where d.emp_no = e.emp_no)

不用exists

select * from employees e 
left join dept_emp d 
on e.emp_no = d.emp_no
where d.emp_no is null