This will update the table with value of hypotenuse . Here is the PHP code to update the table.
require 'config.php'; // Database connection
$sql=$dbo->prepare("update sql_sqrt set H=sqrt(pow(A,2) + pow(B,2))");
if($sql->execute()){
echo "Successfully updated H";
}// End of if profile is ok
else{
print_r($sql->errorInfo()); // if any error is there it will be posted
$msg=" Database problem, please contact site admin ";
}