在MySQL中刪除主鍵需要兩步.

(1)如果有auto_increment，先刪除之;

(2)刪除主鍵約束 primary key

1、alter table table1 modify id int(11);

mysql> desc table1;
+-------+----------+------+-----+---------+----------------+
| Field | Type     | Null | Key | Default | Extra          |
+-------+----------+------+-----+---------+----------------+
| id    | int      | NO   | PRI | NULL    | auto_increment |
| name  | char(20) | NO   |     | NULL    |                |
| age   | char(33) | NO   |     | NULL    |                |
+-------+----------+------+-----+---------+----------------+

#在這里指定id的新類型為int，其他的如自增，自然是刪掉了。。

mysql> alter table table1 modify id int;
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc table1;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id    | int      | NO   | PRI | NULL    |       |
| name  | char(20) | NO   |     | NULL    |       |
| age   | char(33) | NO   |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
3 rows in set (0.00 sec)

2、alter table t9 drop primary key;

#刪除主鍵
mysql> alter table table1 drop primary key;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc table1;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id    | int      | NO   |     | NULL    |       |
| name  | char(20) | NO   |     | NULL    |       |
| age   | char(33) | NO   |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
3 rows in set (0.00 sec)