[打卡]陈洁 内外连接

SELECT e.employee_id,d.department_name FROM employees e,departments d WHERE e.department_id = d.department_id;

# 角度三：内连接和外连接
#SQL92内连接
SELECT e.employee_id,d.department_name FROM employees e,departments d WHERE e.department_id = d.department_id;
#SQL92 外连接：使用+
# 报错：这是因为mysql不支持sq192的外连接
SELECT e.employee_id,d.department_name FROM employees e,departments d WHERE e.department_id = d.department_id(+);
#SQL99
    #SQL99内连接
		#查询员工id和部门名字
SELECT employee_id,department_name FROM employees e JOIN departments d ON e.department_id = d.department_id;
# 加上city
SELECT employee_id,department_name,city from employees e JOIN departments d on e.department_id = d.department_id JOIN locations l on d.location_id = l.location_id;
#SQL99 外连接
    # 左外连接
SELECT employee_id,department_name FROM employees e LEFT OUTER JOIN departments d on e.department_id = d.department_id;
# outer 可以省略掉
SELECT employee_id,department_name FROM employees e LEFT JOIN departments d on e.department_id = d.department_id;
#右链接
SELECT employee_id,department_name FROM employees e right JOIN departments d on e.department_id = d.department_id;