mysql - 如何联合查询两个结构相同的表并且id不重复
1.有两个相同结构的表guangdong_student,shanghai_student,希望联合查询表一，表二，得到表三的结果。使用union会导致id重复，如何做到id自增
2.示例：
表一：guangdong_student
+----+----------+
| id | username |
+----+----------+
| 1 | jhon |
| 2 | may |
| 3 | abcd1111 |
+----+----------+
表二：shanghai_student
+----+----------+
| id | username |
+----+----------+
| 1 | jhon |
| 2 | mike |
| 3 | abcd |
+----+----------+
希望合并后的表：student
+----+----------+
| id | username |
+----+----------+
| 1 | jhon |
| 2 | may |
| 3 | abcd1111 |
| 4 | mike |
| 5 | abcd |
+----+----------+
