Bug #2361 ALTER TABLE ... DROP PRIMARY KEY drops a non-primary key

Description:
ALTER TABLE ... DROP PRIMARY KEY drops a UNIQUE key which is not primary. 
 
I am aware that this is documented behaviour. The MySQL Reference Manual says: 
 
"DROP PRIMARY KEY drops the primary index. If no such index exists, it drops the first 
UNIQUE index in the table. (MySQL marks the first UNIQUE key as the PRIMARY KEY if 
no PRIMARY KEY was specified explicitly.)" 
 
Nevertheless we should fix it because it is unexpected behaviour. 
 
I have the agreement of Brian Aker on this matter. 
 

How to repeat:
mysql> create table t22 (s1 int unique); 
Query OK, 0 rows affected (0.32 sec) 
 
mysql> show create table t22; 
+-------+-------------------------------------------------------------------------------------------------------------------+ 
| Table | Create Table                                                                                                      | 
+-------+-------------------------------------------------------------------------------------------------------------------+ 
| t22   | CREATE TABLE `t22` ( 
  `s1` int(11) default NULL, 
  UNIQUE KEY `s1` (`s1`) 
) ENGINE=MyISAM DEFAULT CHARSET=latin1 | 
+-------+-------------------------------------------------------------------------------------------------------------------+ 
1 row in set (0.00 sec) 
 
mysql> alter table t22 drop primary key; 
Query OK, 0 rows affected (0.29 sec) 
Records: 0  Duplicates: 0  Warnings: 0 
 
mysql> show create table t22; 
+-------+-----------------------------------------------------------------------------------------+ 
| Table | Create Table                                                                            | 
+-------+-----------------------------------------------------------------------------------------+ 
| t22   | CREATE TABLE `t22` ( 
  `s1` int(11) default NULL 
) ENGINE=MyISAM DEFAULT CHARSET=latin1 | 
+-------+-----------------------------------------------------------------------------------------+ 
1 row in set (0.00 sec) 
 

Suggested fix:
Don't drop a unique key if the instruction is to drop a primary key.

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CREATE TABLE person (
    id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
    name CHAR(60) NOT NULL,
    PRIMARY KEY (id)
);

from the above table is created using primary key for 'id' field , then i want drop primary key for the 'id' field in this table. can any 1 tell me how to drop a primary for this table...pls answer me with "syntax " & clear details

venkatesh.vutukuri