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How can we remove PRIMARY KEY constraint from column of existing MySQL table?

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Release: 2023-09-01 17:45:06
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我们如何从现有 MySQL 表的列中删除 PRIMARY KEY 约束?

We can remove PRIMARY KEY constraints from columns of existing tables by using DROP keyword and ALTER TABLE statement.

Example

Suppose we have a table "Player" with a primary key constraint on the "ID" column as follows-
mysql> DESCRIBE Player;

+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| ID    |  int(11)    | NO   | PRI | NULL    |       |
| Name  | varchar(20) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+

2 rows in set (0.04 sec) 
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Now, if we want to delete PRIMARY KEY constraint, then we can use ALTER TABLE statement as shown below-

mysql> alter table Player DROP PRIMARY KEY;
Query OK, 0 rows affected (0.31 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DESCRIBE Player;

+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| ID    |  int(11)  | NO     |     | NULL    |       |
| Name  | varchar(20) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+

2 rows in set (0.04 sec) 
Copy after login

The above result set shows that the PRIMARY KEY constraint on column "ID" has been deleted.

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source:tutorialspoint.com
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