Updated or not Updated $Result=1 Why

[prokhaled]

in this code:

$Sql = "UPDATE Existent SET UserName='$UserName',Existent='$Existent' WHERE Existent<1000";
$Result = mysql_query($Sql);
echo $Result;

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I want to test if row is updated or not but when I echo $Result
if row is updated $Result=1 and If row is not updated $Result=1 also .. Why ?

How can I test if Row is updated or not ?