Question

我正在努力学习加入。但是当我在员工和工资表上尝试完全加入时，它就失败了。为什么会失败？

我已添加解决方案的结果仅供参考。

mysql> select * from employee;
+-----+---------+
| eid | ename   |
+-----+---------+
| 1   | sampath |
| 2   | maclean |
| 3   | sudheer |
+-----+---------+
3 rows in set (0.00 sec)

mysql> select * from Salary;
+------+--------+------+
| sid  | salary | eid  |
+------+--------+------+
| 1001 |   5000 | 2    |
| 1002 |  70000 | 3    |
| 1003 |  70000 | 3    |
+------+--------+------+
3 rows in set (0.00 sec)

mysql> select employee.eid, employee.ename, Salary.salary from employee JOIN Salary  on employee.eid=Salary.eid;
+-----+---------+--------+
| eid | ename   | salary |
+-----+---------+--------+
| 2   | maclean |   5000 |
| 3   | sudheer |  70000 |
| 3   | sudheer |  70000 |
+-----+---------+--------+
3 rows in set (0.00 sec)

mysql> select employee.eid, employee.ename, Salary.salary from employee LEFT JOIN Salary  ON employee.eid=Salary.eid;
+-----+---------+--------+
| eid | ename   | salary |
+-----+---------+--------+
| 1   | sampath |   NULL |
| 2   | maclean |   5000 |
| 3   | sudheer |  70000 |
| 3   | sudheer |  70000 |
+-----+---------+--------+
4 rows in set (0.00 sec)

mysql> select employee.eid, employee.ename, Salary.salary from employee RIGHT JOIN Salary  ON employee.eid=Salary.eid;
+------+---------+--------+
| eid  | ename   | salary |
+------+---------+--------+
| 2    | maclean |   5000 |
| 3    | sudheer |  70000 |
| 3    | sudheer |  70000 |
+------+---------+--------+
3 rows in set (0.00 sec)

的MySQL＆GT;选择employee.eid，employee.ename，Salary.salary from employee FULL JOIN Salary on employee.eid = Salary.eid; ERROR 1054（42S22）：'字段列表'中的未知列'employee.eid' MySQL的＆GT;

更新：以下是Left Join Union Right Join的结果

mysql> SELECT * FROM employee e
    -> LEFT JOIN Salary s ON e.eid = s.eid
    -> UNION
    -> SELECT * FROM employee e
    -> RIGHT JOIN Salary s ON e.eid = s.eid;
+------+---------+------+--------+------+
| eid  | ename   | sid  | salary | eid  |
+------+---------+------+--------+------+
| 1    | Rai     | NULL |   NULL | NULL |
| 2    | pinto   | 1001 |  50000 | 2    |
| 3    | sudheer | 1002 |  70000 | 3    |
| 3    | sudheer | 1003 |  70000 | 3    |
+------+---------+------+--------+------+
4 rows in set (0.00 sec)

Answer 1

MySQL不支持FULL OUTER JOIN关键字。仅支持LEFT JOIN和RIGHT JOIN。

你可以尝试这样做来模仿：

SELECT * FROM employee e
LEFT JOIN salary s ON e.eid = s.eid
UNION
SELECT * FROM employee e
RIGHT JOIN salary s ON e.eid = s.eid

Answer 2

mysql不支持完全加入。

检查以下问题希望它能帮助您解决问题:)

MySQL FULL JOIN not working but RIGHT and LEFT join works

完全加入Mysql失败

2 个答案: