....snip....
my $query1 = "SELECT field1,field2,field3 FROM table WHERE `flag`=0";
my $sth = $dbh->prepare($query1);
$sth->execute();

# Loop query to build an array
# this pulls each row into an 
# array that we can manipulate
while ( ($var1,$var2,$var3) = $sth->fetchrow_array() ) {
# update the flag field to reflect the ad has been ehnanced
   my $query2 = "UPDATE table SET `flag`='1' WHERE field1=?";
   my $sth2 = $dbh->prepare($query2);
   $sth2->execute($var1);
   ....snip....   
   }