How to delete primary key in mysql?

After setting a primary key in a table, what should I do if I want to delete the primary key? The following article will introduce to you how to delete the primary key in MySQL. I hope it will be helpful to you.

First let’s take a look at the syntax of deleting the primary key:

ALTER  TABLE  TABLE_NAME  DROP  PRIMARY  KEY;

There are two situations to consider when deleting the primary key in MySQL:

1. The primary key column does not have any constraints and the primary key can be deleted directly.

Example:

mysql> create table test1_3(
    -> id int not null primary key,
    -> name char(10)
    -> );
Query OK, 0 rows affected (0.01 sec)

We can directly use drop to delete the primary key

mysql> alter table test1_3 drop primary key;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

2. If It is the primary key of auto-increment (AUTO_INCREMENT attribute)

Example:

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)

If deleted directly, an error will be reported

mysql> alter table test1_2 drop primary key;

Output:

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

The attributes of the column are still With AUTO_INCREMENT, you must first remove the automatic growth attribute of this column before you can delete the primary key.

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

The above is the detailed content of How to delete primary key in mysql?. For more information, please follow other related articles on the PHP Chinese website!