ALTER table - adding AUTOINCREMENT in MySQL

Question

I created a table in MySQL with on column itemID.

After creating the table, now I want to change this column to AUTOINCREMENT.

How can this be done using ALTER statements?

Table definition:

ALLITEMS (itemid int(10) unsigned, itemname varchar(50))

I am using the following code but it is throwing a syntax error

Error: syntax incorrect.

ALTER TABLE allitems MODIFY itemid INT(10) UNSIGNED AUTOINCREMENT;  

Answer 1

CREATE TABLE ALLITEMS(     itemid INT(10)UNSIGNED,     itemname VARCHAR(50) );  ALTER TABLE ALLITEMS CHANGE itemid itemid INT(10)AUTO_INCREMENT PRIMARY KEY;  DESC ALLITEMS;  INSERT INTO ALLITEMS(itemname) VALUES     ('Apple'),     ('Orange'),     ('Banana');  SELECT     * FROM     ALLITEMS; 

I was confused with CHANGE and MODIFY keywords before too:

ALTER TABLE ALLITEMS CHANGE itemid itemid INT(10)AUTO_INCREMENT PRIMARY KEY;  ALTER TABLE ALLITEMS MODIFY itemid INT(5); 

While we are there, also note that AUTO_INCREMENT can also start with a predefined number:

ALTER TABLE tbl AUTO_INCREMENT = 100; 

Answer 2

The syntax:

   ALTER TABLE `table1` CHANGE `itemId` `itemId` INT( 11 ) NOT NULL AUTO_INCREMENT  

But the table needs a defined key (ex primary key on itemId).