Trying to remove a primary key from MySQL table

Question

Edit: Not sure why this is marked as a duplicate. The error I am getting is different

I am trying to remove a primary key definition but am receiving an error for some reason.

mysql> ALTER TABLE `aux_sponsors` DROP PRIMARY KEY;
ERROR 1091 (42000): Can't DROP 'PRIMARY'; check that column/key exists
mysql> desc aux_sponsors;
+-------------+--------------+------+-----+---------+-------+
| Field       | Type         | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+-------+
| unit        | varchar(8)   | NO   |     | MF      |       |
| code        | varchar(32)  | NO   | PRI | NULL    |       |
| userid      | varchar(32)  | NO   |     |         |       |
| fullName    | varchar(64)  | NO   |     |         |       |
| department  | varchar(255) | NO   |     |         |       |
| description | varchar(255) | NO   |     | NULL    |       |
+-------------+--------------+------+-----+---------+-------+
6 rows in set (0.01 sec)

Am I doing something wrong here? I simply want no more primary key in this table.

mysql> SHOW CREATE TABLE aux_sponsors;
+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table        | Create Table                                                                                                                                                                                                                                                                                                                                                |
+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| aux_sponsors | CREATE TABLE `aux_sponsors` (
  `unit` varchar(8) NOT NULL DEFAULT 'MF',
  `code` varchar(32) NOT NULL,
  `userid` varchar(32) NOT NULL DEFAULT '',
  `fullName` varchar(64) NOT NULL DEFAULT '',
  `department` varchar(255) NOT NULL DEFAULT '',
  `description` varchar(255) NOT NULL,
  UNIQUE KEY `code` (`code`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 |
+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

Answer 1

You don't have a PRIMARY KEY; you have a UNIQUE key. So, you can't do this:

ALTER TABLE `aux_sponsors` DROP PRIMARY KEY

Instead, just do

ALTER TABLE `aux_sponsors` DROP KEY `code`

DESC (a/k/a DESCRIBE) is not a true MySQL feature; according to the docs, "The DESCRIBE statement is provided for compatibility with Oracle."

More from the documentation:

A UNIQUE index may be displayed as PRI if it cannot contain NULL values and there is no PRIMARY KEY in the table. A UNIQUE index may display as MUL if several columns form a composite UNIQUE index; although the combination of the columns is unique, each column can still hold multiple occurrences of a given value.

In your case, the column code is NOT NULL and is the only column in a UNIQUE key, so DESC is showing it as PRI. Because of this type of problem, it's better to use SHOW INDEX to find out the types of keys on a table.