php - While loop in FPDF retrieve data only first time.It prints the table in pdf perfectly but doesn't input the data retrieved after first time -

i printing table filled data retrieved database in pdf using fpdf library. want code run until end , print data of students in groups in table.it retrieving , printing data first group other groups prints table , doesn't populate data. here code.

session_start(); require ('../make_db_connection.php'); require ("../fpdf/fpdf.php"); $pdf=new fpdf('p','mm','a4'); $res = $conn->query("select * student_data"); $num=$res->num_rows; while ($num > 0) {     $pdf->addpage();      if ($num != 0)     {         $row = $res->fetch_assoc();         $title=$row['title'];         $date=$row['sub_date'];         $supervisor=$row['supervisor'];         $res = $conn->query("select name,roll_no,abstract student_data title='".$title."' , supervisor='".$supervisor."'");     }     $pdf->setfillcolor(232,232,232);     $pdf->setmargins(30,0,20);     $pdf->setfont('times','b',14);     $pdf->cell(0,10,'',0,1);     $pdf->cell(0,7,"fyp evaluation sheet",0,1,'c');     $pdf->setfont('times','b',13);     $pdf->cell(0,4,'',0,1);     $pdf->cell(40,7,"gr#:",0,0,'l');     $pdf->cell(30,7,"project title:",0,0,'l');     $pdf->setfont('times','',11);     $pdf->multicell(90,7,$title,'','l',false);     //table     $pdf->setfont('times','b',13);     $pdf->cell(0,4,'',0,1);     $pdf->cell(40,7,"individuals:",0,0,'l');     $pdf->cell(0,10,'',0,1);     $x=$pdf->getx();     $y=$pdf->gety();     $pdf->multicell(35,10, 'reg#','lrtb','c',true);     $pdf->setxy($x+35,$y);     $pdf->multicell(70,10, 'name','ltb','c', true);     $pdf->setxy($x+105,$y);     $pdf->multicell(50,10, 'marks & comments','lrtb','c', true);     $pdf->multicell(0,0, '','r',false);     $pdf->setfont('times','',10);     $x=$pdf->getx();     $y=$pdf->gety();     $row = $res->fetch_assoc();     $student1=$row['name'];      $student1_rollno=$row['roll_no'];     $num=$num-1;     $pdf->multicell(35,8,$student1_rollno,'lrb','c',0);     $pdf->setxy($x+35,$y);     $pdf->multicell(70,8,$student1,'b','c', 0);     $pdf->setxy($x+105,$y);     $pdf->multicell(50,8,'','lrb','l', 0);     $x=$pdf->getx();     $y=$pdf->gety();     $row = $res->fetch_assoc();     if($row)     {         $student2=$row['name'];          $student2_rollno=$row['roll_no'];         $pdf->multicell(35,8,$student2_rollno,'lrb','c',0);         $pdf->setxy($x+35,$y);         $pdf->multicell(70,8,$student2,'b','c', 0);         $pdf->setxy($x+105,$y);         $pdf->multicell(50,8,'','lrb','l', 0);         $num=$num-1;     }     $pdf->multicell(100,8, 'note: please fill form , submit name ,   signature.','','l', 0);  } ob_end_clean(); $pdf->output(); 

what doing wrong in code?i can't figure out!

i'll put answer here since comment on op worked out.

you used $res variable store results query within while loop, overwrites stored result.