外连接（FULL JOIN）
mysql不支持FULL JOIN，但是可以用 left join union right join代替
 A∪B |
 A∪B – A∩B |
| #查询所有部门信息和员工信息
SELECT did,dname,eid,ename FROM t_department LEFT OUTER JOIN t_employee ON t_department.did = t_employee.dept_id UNION SELECT did,dname,eid,ename FROM t_department RIGHT OUTER JOIN t_employee ON t_department.did = t_employee.dept_id; |
#查询所有没有员工的部门和没有分配部门的员工
SELECT did,dname,eid,ename FROM t_department LEFT OUTER JOIN t_employee ON t_department.did = t_employee.dept_id WHERE t_employee.dept_id IS NULL UNION SELECT did,dname,eid,ename FROM t_employee LEFT OUTER JOIN t_department ON t_department.did = t_employee.dept_id WHERE t_employee.dept_id IS NULL; |
 |
 |
想要了解跟多关于Java培训课程内容欢迎关注尚硅谷Java培训课程，尚硅谷除了这些技术文章外还有免费的高质量Java培训课程视频供广大学员下载学习
