PHP - suma de columa en php

$query=mysql_query("select total from salidas");

$suma=0;

while($sumar=mysql_fetch_assoc($query))

{

$suma=$suma+$sumar["total"];

}

echo $suma;

$query=mysql_query("select total from salidas where num_placa=''$num_placa");

$suma=0;

while($sumar=mysql_fetch_assoc($query))

{

$suma=$suma+$sumar["total"];

}

echo $suma;

$query=mysql_query("select total from salidas where num_placa = $num_placa");

$suma=0;

while($sumar=mysql_fetch_assoc($query))

{

$suma += $sumar["total"];

}

echo $suma;

$query=mysql_query("select SUM(total) as sumaTotal from salidas where num_placa = $num_placa");

$suma = 0;

while($row=mysql_fetch_assoc($query))

{

$suma += $row["sumaTotal"];

}

echo $suma;