how would I...

viveleroi0

If an sql query in an IF statement like:

if ProductNumber equals any NumberField from this table, display error

else add product to cart

hrosas

I think you should use somethog like:
$SQKQuery = "SELECT item FROM table WHERE colum=$any_number";
then execute (mysql_query);
if ( mysql_fetch_row()) echo "error";
else{
$SQLQUery ="UPDATE .......";
mysql_query($SQLQUery );
}