some problem to add a mysql field value to an array

how can i read a mysql table of two fields and test if the first field has a
value then add the second value to an array

I try this but it doesn't works

while ($row=mysql_fetch_array($result))
{
for ($i=0; $i< mysql_num_fields($result); $i++)
if ($row['CampoChiave']=='true')
$TempArray[ ]=$row['NomeCampo'];
}

What is the "for" loop for if you do not use it's index ($i)?

You are testing if CampoChiave has a string value of 'true'.
You wrote that you want to test if it has any value. You
may do it like this:

if (isset($row['CampoChiave']) && ($row['CampoChiave']!=''))
$TempArray[]=$row['NomeCampo'];


Hilarion

PS.: I do not use MySQL, so my suggestions are general PHP related
and may not be sufficient.