Adding auto_increment after table creation

Say the table is created like this,

mysql> CREATE TABLE customer (id int, fname varchar(20));

The above table would be created without having an index. If there is a need to make id primary key, then

mysql> ALTER TABLE customer ADD PRIMARY KEY (id);

Then adding auto_increment would be as:

mysql> ALTER TABLE customer CHANGE id id int NOT NULL AUTO_INCREMENT;

Trying to assign auto_increment before making it a primary key – if it is not already done during creation, might produce an error. Actually trying to drop the primary key before neutralizing the auto_increment would also might create an error.
The following query would take out the auto_increment part from the table

ALTER TABLE customer CHANGE id id int not null;

And, of course, after this it is possible to drop primary key.