Composite Primary Key and Auto_Increment [duplicate] - mysql

Question

This question already has answers here:
mysql two column primary key with auto-increment
(4 answers)
Closed 9 years ago.
I'm trying to do the composite key with one of them auto incrementing, but when I try to enter a new row it just continue the sequential.
Here's the example of what happens:
Item_1 | Item_2
1 | 1
1 | 2
2 | 3
2 | 4
2 | 5
Here's the example of what I want:
Item_1 | Item_2
1 | 1
1 | 2
2 | 1
2 | 2
2 | 3
I create the table this way:
CREATE TABLE IF NOT EXISTS `usuarios` (
`cod_user` int(11) NOT NULL AUTO_INCREMENT,
`cod_user_emp` int(11) NOT NULL,
PRIMARY KEY (`cod_user`,`cod_user_emp`),
UNIQUE KEY `user` (`user`),
KEY `cod_user` (`cod_user`)
);
Edit
I resolved the problem doing a server sided php validation.
$result = $db->query("SELECT * FROM usuarios WHERE cod_user_emp=\"$emp\" ORDER BY cod_user DESC LIMIT 1");
while($row=$result->fetch_array()){
$cod2 = $row['cod_user']+1;
}

Answer 1

Remove that AUTO_INCREMENT column,
CREATE TABLE IF NOT EXISTS `usuarios`
(
`cod_user` int(11) NOT NULL,
`cod_user_emp` int(11) NOT NULL,
PRIMARY KEY (`cod_user`,`cod_user_emp`) -- <<== this is enough
);
And can create a Stored Procedure that increments Item_2 for every Item_1.
DELIMITER $$
CREATE PROCEDURE InsertRecord(IN ItemA INT)
BEGIN
SET #max_id = (
SELECT COALESCE(MAX(Item_2), 0) + 1
FROM TableName
WHERE Item_1 = ItemA
);
INSERT INTO tableName(Item_1, Item_2)
VALUES(ItemA, #max_id)
END $$
DELIMITER ;
and call it like this,
CALL InsertRecord(2);