Your code is not complete, but I will try to solve. You just have to do checking on $cell['bpm_number']
like you do on $cell['material_code']
.
$cekmaterial_code = "";
$bpm_number = "";
for (...) {
...
if ($bpm_number !== $cell['bpm_number'])
$bpm_number = $cell['bpm_number'];
echo "<td>$cell[bpm_number]</td><td>$cell[quantity_dely</td>";
} else {
echo "<td></td><td>$cell[quantity_dely]</td>";
}
..
}