获取员工其当前的薪水比其manager当前薪水还高的相关信息，当前表示to_date=’9999-01-01’,
结果第一列给出员工的emp_no，
第二列给出其manager的manager_no，
第三列给出该员工当前的薪水emp_salary,
第四列给该员工对应的manager当前的薪水manager_salary
create table dept_emp (
emp_no int(11) not null,
dept_no char(4) not null,
from_date date not null,
to_date date not null,
primary key (emp_no,dept_no));
create table dept_manager (
dept_no char(4) not null,
emp_no int(11) not null,
from_date date not null,
to_date date not null,
primary key (emp_no,dept_no));
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));
这类直接暴力使用where，注意题目的条件。
select e.emp_no as emp_no,m.emp_no as manager_no,s1.salary as emp_salary,s2.salary as manager_salary from salaries s1,salaries s2,dept_emp e,dept_manager m where e.emp_no=s1.emp_no and m.emp_no=s2.emp_no and e.dept_no=m.dept_no and e.emp_no!=m.emp_no and s1.salary>s2.salary and e.to_date='9999-01-01' and m.to_date='9999-01-01' and s1.to_date='9999-01-01' and s2.to_date='9999-01-01'
