sql.8

找出所有员工当前(to_date='9999-01-01')具体的薪水salary情况，对于相同的薪水只显示一次,并按照逆序显示
CREATE TABLE salaries (
emp_no int(11) NOT NULL,
salary int(11) NOT NULL,
from_date date NOT NULL,
to_date date NOT NULL,
PRIMARY KEY (emp_no,from_date));

解释

 题目没有什么难度，主要讨论一下去重的问题

方法一

1. 使用group by

select salary 
from salaries 
where to_date = '9999-01-01'
group by salary
order by salary desc 

方法二

2. 使用distinct关键字

select dintinct salary 
from salaries 
where to_date = '9999-01-01'
order by salary desc