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SELECT employee_id,last_name,department_name,city
FROM employees e, departments d, locations l
WHERE e.department_id=d.department_id
AND d.location_id=l.location_id;

SELECT* FROM job_grades;


举例：查询名字、月薪，和相应等级

SELECT e.last_name,e.salary,j.grade_level
FROM employees e,job_grades j
WHERE e.salary BETWEEN j.lowest_sal
and j.highest_sal;

SELECT e.last_name,e.salary,j.grade_level
FROM employees e,job_grades j
WHERE e.salary >= j.lowest_sal
and e.salary<= j.highest_sal;

#自连接（自我引用）VS 非自连接

SELECT * FROM employees;

#查询员工ID，员工姓名及其管理者的ID和姓名

SELECT emp.employee_id,emp.last_name,mgr.employee_id,mgr.last_name
FROM employees emp,employees mgr
WHERE emp.manager_id=mgr.employee_id;