mysql> create table hj89 (mem_id integer primary key, mem_username varchar(32), parent_cp_member_active varchar(32));
Query OK, 0 rows affected (0.17 sec)

mysql> insert into hj89 values(32687, '张三', 32457);
Query OK, 1 row affected (0.06 sec)

mysql> insert into hj89 values(32457, '李四', 32687);
Query OK, 1 row affected (0.05 sec)

mysql> select mem_id, mem_username, (select mem_username from hj89 where mem_id = c.parent_cp_member_active) from hj89 c;
+--------+--------------+--------------------------------------+
| mem_id | mem_username | (select mem_username from hj89 where mem_id = c.parent_cp_member_active) |
+--------+--------------+--------------------------------------+
|  32457 | 李四         | 张三                                                                     |
|  32687 | 张三         | 李四                                                                     |
+--------+--------------+--------------------------------------+
2 rows in set (0.03 sec)