Merge Cell values with PHPExcel - PHP

I have a simple table like:

- id 
- first_name
- last_name
- email
- phone

I'm using PHPExcel to export my data in XLS format

    $rowNumber = 1;
    while ($row = mysql_fetch_row($result)) {
       $col = 'A';
       foreach($row as $cell) {
          $objPHPExcel->getActiveSheet()->setCellValue($col.$rowNumber,$cell);
          $col++;
       }
       $rowNumber++;
   }

Now I want to merge the two fields first_name & last_name in one Cell

I tried:

$rowNumber = 1;
   while ($row = mysql_fetch_row($result)) {
   $objPHPExcel->getActiveSheet()->setCellValue('A'.$rowNumber,$row['id'])
                                 ->setCellValue('B'.$rowNumber,$row['first_name'])
                                 ->setCellValue('C'.$rowNumber,$row['last_name']);                                                                  
   $rowNumber++;
}

But I get errors and don't works. Any help?

There is a specific method to do this:

$objPHPExcel->getActiveSheet()->mergeCells('A1:C1');

You can also use:

$objPHPExcel->setActiveSheetIndex(0)->mergeCells('A1:C1');

That should do the trick.

Try this

$objPHPExcel->getActiveSheet()->mergeCells('A1:C1');

$this->excel->setActiveSheetIndex(0)->mergeCells("A".($p).":B".($p)); for dynamic merging of cells