<?php
$connect = mysqli_connect("localhost", "root", "", "repo");
$q = "SELECT SUM(importe_fac) as total , YEAR(fecha_fac) as anio FROM facturas GROUP BY YEAR(fecha_fac) ORDER BY id_fac ASC";
$r = mysqli_query($connect, $q);
$chart_data = '';
while($row = mysqli_fetch_array($r))
{
 $chart_data .= "{ y:'".$row["anio"]."', Total:".$row["total"]."}, ";
}
$chart_data = substr($chart_data, 0, -2);
?>