
        
        
            
                
                
                    ALTER TABLE table_name DROP PRIMARY KEY, ADD PRIMARY KEY (column_name);

Example

Given a table called info with the column name as the primary key:


        
        
            
                
                
                    DESCRIBE info;
                
            
            +-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| name  | varchar(20) | NO   | PRI | NULL    |       |
| age   | int         | YES  |     | NULL    |       |
| hobby | varchar(20) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+

To set the column age as the new primary key:


        
        
            
                
                
                    ALTER TABLE info DROP PRIMARY KEY, ADD PRIMARY KEY (age);

Here we first drop the current primary key and then in the latter half of the statement we newly set the primary key on the age column.

To check the primary key is now updated:


        
        
            
                
                
                    DESCRIBE info;
                
            
            +-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| name  | varchar(20) | NO   |     | NULL    |       |
| age   | int         | NO   | PRI | NULL    |       |
| hobby | varchar(20) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+