Update updating fields "incorrectly"

SQL :

$sql = "
UPDATE atributos_prod SET codigo='$codigo', descricao='$descricao', preco='$preco' 
WHERE id='$id'
";

The values entered are captured as follows:

$postdata = file_get_contents("php://input");
$request = json_decode($postdata);

$id                     = $request->id;
$codigo                 = $request->item->codigo; 
$descricao              = $request->item->descricao; 
$preco                  = $request->item->preco; 

JSON object $postdata :

{
    "0": {
        "codigo": "5",
        "descricao": "Bobina",
        "preco": "5.0"
    },
    "1": {
        "codigo": "10",
        "descricao": "Copo",
        "preco": "0.5"
    }
}

[The page where the SQL command is run in a 2 second interval]

1st UPDATE [2sec] execution:

|id|codigo|descricao|preco
|1 |   5  | Bobina  | 5.0
|2 |  10  | Copo    | 0.5

2nd execution of UPDATE [4sec]:

|id|codigo|descricao|preco
|1 |  5   | Bobina  | 5.0
|2 |  5   | Bobina  | 5.0

3rd UPDATE [6sec] execution:

|id|codigo|descricao|preco
|1 |   5  | Bobina  | 5.0
|2 |  10  | Copo    | 0.5

that is, the "second" execution of update is performed incorrectly.

Editing :

print_r($request) :

stdClass Object
(
    [item] => stdClass Object
        (
            [codigo] => 5
            [descricao] => Bobina
            [preco] => 5.0
        )

    [id] => 2
)

stdClass Object
(
    [item] => stdClass Object
        (
            [codigo] => 10
            [descricao] => Copo
            [preco] => 0.5
        )

    [id] => 2
)