How to replace NULL with zero?

mysql_query("SELECT sum(qty) FROM table WHERE lid='" . $row['lid'] . "' AND transtype_id='ALL'");

Code (php):

Should there be no records tagged with 'ALL', mysql returns a NULL. Instead of NULL, how do I make it return me a ZERO as in 0.

Thanks.

 

$var = mysql_query.........

if $var = null

$var = '0';

.....

??

 

what difference does it make? Do this instead:

$sql=@mysql_query("SELECT sum(qty) FROM table WHERE lid='" . $row['lid'] . "' AND transtype_id='ALL'"); 
if (!$sql) exit;

Code (markup):

 

Sorry.. I should have been more specific. I'm using the mysql_query command with Maani's PHP Chart.
http://www.maani.us/charts/index.php?menu=Tutorial&submenu=Chart_Data

$chart [ 'chart_data' ][ $row1 ][ $count ]=mysql_query("SELECT sum(qty) FROM table WHERE lid='" . $row['lid'] . "' AND transtype_id='ALL'");

Code (php):

If the query returns a NULL, the chart will be distorted.

 

UPDATE table SET field=0 WHERE field IS NULL;

 

Returns 0 if sum(qty) is null
mysql_query("SELECT COALESCE(sum(qty),0) FROM table WHERE lid='" . $row['lid'] . "' AND transtype_id='ALL'");