สอบถามเกี่ยวกับค่า string แตกเป็น array ด้วยคำสั่ง explode

<?php 
/* Database connection start */
$servername = "localhost";
$username = "root";
$password = "4321";
$dbname = "salecentral";

$conn = mysqli_connect($servername, $username, $password, $dbname) or die("Connection failed: " . mysqli_connect_error());
mysqli_set_charset($conn,"utf8");
/* Database connection end */


// storing  request (ie, get/post) global array to a variable  
$requestData= $_REQUEST;


$columns = array( 
// datatable column index  => database column name
	0 =>'ptype',
	1 =>'date',
	2 =>'name_partner',
	3 =>'po_no', 
	4 => 'qt_no',
	5 => 'com',
	6 => 'all_file',
	7 => 'Ename'
);

// getting total number records without any search
$sql = "......";
$query=mysqli_query($conn, $sql) or die("employee-grid-data.php: get employees");
$totalData = mysqli_num_rows($query);
$totalFiltered = $totalData;  // when there is no search parameter then total number rows = total number filtered rows.

$sql = "......";
if( !empty($requestData['search']['value']) ) {   // if there is a search parameter, $requestData['search']['value'] contains search parameter
	$sql.=" AND ( ptype LIKE '%".$requestData['search']['value']."%' ";    
	$sql.=" OR date LIKE '%".$requestData['search']['value']."%' ";
	$sql.=" OR name_partner LIKE '%".$requestData['search']['value']."%' ";
	$sql.=" OR po_no LIKE '%".$requestData['search']['value']."%' ";
	$sql.=" OR qt_no LIKE '%".$requestData['search']['value']."%' ";
	$sql.=" OR com LIKE '%".$requestData['search']['value']."%' ";
	$sql.=" OR Ename LIKE '%".$requestData['search']['value']."%' )";
	
}
$query=mysqli_query($conn, $sql) or die("employee-grid-data.php: get employees");
$totalFiltered = mysqli_num_rows($query); // when there is a search parameter then we have to modify total number filtered rows as per search result. 
$sql.=" ORDER BY ". $columns[$requestData['order'][0]['column']]."   ".$requestData['order'][0]['dir']."  LIMIT ".$requestData['start']." ,".$requestData['length']."   ";
/* $requestData['order'][0]['column'] contains colmun index, $requestData['order'][0]['dir'] contains order such as asc/desc  */	
$query=mysqli_query($conn, $sql) or die("employee-grid-data.php: get employees");


$data = array();
while( $row=mysqli_fetch_array($query) ) {  // preparing an array
	$idPO= $row["idPO"];
	$nestedData=array();
	if($row['ptype']=='po') { $nestedData[] = "PO";} 
	if($row['ptype']=='ใบเคลม') { $nestedData[] = "ใบเคลม";} 
	
	if($row['com']=='CC') { $nestedData[] = "<div style='color: red;opacity:0.0;'>$row[com]</div><img src='images/central.png' height='40px'/>";} 
			if($row['com']=='CL') { $nestedData[] = "<div style='color: red;opacity:0.0;'>$row[com]</div><img src='images/clwheel.png' height='40px'/>";}
			if($row['com']=='DS') { $nestedData[] = "<div style='color: red;opacity:0.0;'>$row[com]</div><img src='images/dreamshop.png' height='40px'/>";}

	list($Year,$month,$day) = explode("-",$row['date']);
    $nestedData[] = (int)$day."/".(int)$month."/".($Year+543);
	
	$nestedData[] = $row["po_no"];
	if($row['qt_no']!= "ประวัติลูกค้า" && $row['qt_no']!= "ข้อมูลSale"){
	if (strpos($row['qt_no'],'Rev'))
	{ $nestedData[] = "<a class='example1' href='viewEdit$row[com].php?idx=$row[qt_no]'>$row[qt_no]</a>";}
	else{ $nestedData[] = "<a class='example1' href='view$row[com].php?idx=$row[qt_no]'>$row[qt_no]</a>";}
	} else { $nestedData[] = $row['qt_no'];}
	$nestedData[] = $row["name_partner"];
	/* $row["all_file"] คือ ไฟล์ที่มีทั้งหมดของใบ po นั้น แล้วแต่ว่า poหนึ่งๆจะมีกี่ใบก็ได้ GROUP_CONCAT( po_detail.file ) AS all_file ตย. เช่น po.no=PO0005941 มี1ไฟล์ ชื่อ 181125591.jpg  $row["all_file"]=181125591.jpg
po.no=F31591 มี2ไฟล์ ชื่อ 181125592.jpg,181125593.jpg  $row["all_file"]=181125592.jpg,181125593.jpg
*/
	$array = explode(',', $row["all_file"]);
	foreach(array_unique($array ) as $val){
	list($name,$type) = explode(".",$val);
     if ($type =='pdf') { $nestedData[] = "<a class='example1' href='images/po/$val'><img src='images/po/PDF-icon.png' align='left' width='60px'/></a>";}
	 else {	 $nestedData[] = "<a class='example1' href='preview.php?type=po&images=$val'><img src='images/po/$val' width='60px'/></a>";}
	
	}
	/*list($name,$type) = explode(".",$row['file']);
     if ($type =='pdf') { $nestedData[] = "<a class='example1' href='images/po/$row[file]'><img src='images/po/PDF-icon.png' align='left' width='60px'/></a>";}
	 else {	 $nestedData[] = "<a class='example1' href='preview.php?type=po&images=$row[file]'><img src='images/po/$row[file]' width='60px'/></a>";}
	*/$nestedData[] = $row['Ename']." (".$row['Enname'].")"; 
	$nestedData[] = "<a class='example1' href='checkEdit.php?idx=$idPO&po=po' target='_self'><img src='../images/edit.png' width='30' title='แก้ไข' border='0' ></a>";
	$data[] = $nestedData;
}



$json_data = array(
			"draw"            => intval( $requestData['draw'] ),   // for every request/draw by clientside , they send a number as a parameter, when they recieve a response/data they first check the draw number, so we are sending same number in draw. 
			"recordsTotal"    => intval( $totalData ),  // total number of records
			"recordsFiltered" => intval( $totalFiltered ), // total number of records after searching, if there is no searching then totalFiltered = totalData
			"data"            => $data   // total data array
			);

echo json_encode($json_data);  // send data as json format
?>