首先我们来看看删除主键的语法：
ALTER TABLE TABLE_NAME DROP PRIMARY KEY;
在MySQL中删除主键要考虑两种情况：
1、主键列不带任何约束，可以直接删除主键的情况
mysql> create table test1_3(
-> id int not null primary key,
-> name char(10)
-> );
Query OK, 0 rows affected (0.01 sec)
我们可以直接使用drop来删除主键
mysql> alter table test1_3 drop primary key;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
2、如果是自增（AUTO_INCREMENT属性）的主键
mysql> create table test1_2(
-> id int not null auto_increment,
-> name char(10),-> primary key(id)
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> desc test1_2;
+-------+----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | char(10) | YES | | NULL | |
+-------+----------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
如果直接删除，会报错
mysql> alter table test1_2 drop primary key;
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
#这说明此列是自动增长列，无法直接删除
列的属性还带有AUTO_INCREMENT，那么要先将这个列的自动增长属性去掉，才可以删除主键。
mysql> alter table test1_2 modify id int;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> alter table test1_2 drop primary key;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
地址：https://www.php.cn/mysql-tutorials-418313.html