mysql> create table zc_test2(id int);
Query OK, 0 rows affected (1.37 sec)
mysql> insert into zc_test2 values (10),(9),(8),(7),(6);
Query OK, 5 rows affected (0.04 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from zc_test2;
+------+
| id |
+------+
| 10 |
| 9 |
| 8 |
| 7 |
| 6 |
+------+
5 rows in set (0.00 sec)
mysql> ALTER TABLE zc_test2 add id2 int;
Query OK, 0 rows affected (2.84 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> select * from zc_test2;
+------+------+
| id | id2 |
+------+------+
| 10 | NULL |
| 9 | NULL |
| 8 | NULL |
| 7 | NULL |
| 6 | NULL |
+------+------+
5 rows in set (0.00 sec)
mysql> alter table zc_test2 change id2 id2 int NOT NULL AUTO_INCREMENT;
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
mysql> alter table zc_test2 change id2 id2 int NOT NULL AUTO_INCREMENT primary key;
Query OK, 5 rows affected (1.34 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from zc_test2;
+------+-----+
| id | id2 |
+------+-----+
| 10 | 1 |
| 9 | 2 |
| 8 | 3 |
| 7 | 4 |
| 6 | 5 |
+------+-----+
5 rows in set (0.00 sec)
