sql">#2.非等值连接


#案例1:查询员工的工资和工资级别(另一张表)
SELECT salary,grade_level
FROM employees e,job_grades g
WHERE salary BETWEEN g.`lowest_sal`AND g.`highest_sal` ;

#3.自连接

#案例:查询 员工名 和上级名名称
SELECT e.employee_id,e.last_name, m.employee_id,m.last_name
FROM employees e ,employees m
WHERE e.`manager_id`=m.`employee_id`;