[mySql] duplicazione record

[techno]

Salve ho questa query:

$codeproduct=trim($_GET["codeproduct"]);
$sql="INSERT INTO magazine (ID,CodeProduct,Description_IT,Specifications_IT,Price,VAT, Stock) ";
$sql.="SELECT '$id',CodeProduct,Description_IT,Specifications_IT,Price,VAT,Stock FROM magazine WHERE ID='$codeproduct'"; if(!mysql_query($sql)){
... 

Ma non duplica i record e non capisco il perchè.