Update form and save update in one page

<?php
$db=mysqli_connect("localhost","root","","mycompanyhr");
if($db==true){
    echo "Connection succeed!!!<br>";
}
else{
    echo "Connection fail!!!<br>";
}
//get the empno
$empno=$_GET['id'];
//develop the SQL command
$q="select * from employee
    where EMPNO='$empno'";
    
//execute SQL command
$rs=mysqli_query($db,$q);
if($rs==false){
  echo ("Query cannot be executed!<br>");
  echo ("SQL Error : ".mysqli_error($db));
}
//extract data from resultset
$rekod=mysqli_fetch_array($rs);
$fullname=$rekod['FULLNAME'];
$dept=$rekod['DEPT'];
$gender=$rekod['GENDER'];
//populate old data in a form
?>
Update record 
<form name="frmupdate" method="get" action=""> 
Employee No 
<input type="text" name="txtempno" maxlength=6
  value="<?=$empno?>"><br> 
Fullname 
<input type="text" name="txtname"
  value="<?=$fullname?>"><br> 
Department code 
<input type="text" name="txtdeptcode" maxlength=3
  value="<?=$dept?>"><br> 
Gender 
<input type="text" name="txtgender"
  value="<?=$gender?>">
<br>
<input type="submit" value="Save Record"> 
</form> 
<?php
$empno=$_GET['txtempno'];
$fullname=$_GET['txtname'];
$dept=$_GET['txtdeptcode'];
$gender=$_GET['txtgender'];
if ($empno!=NULL){
  $db2=mysqli_connect("localhost","root","","mycompanyhr");
  if($db2==true){
    echo "Connection succeed!!!<br>";
  }
  else{
    echo "Connection fail!!!<br>";
  }
  
  $sql2="update employee
      set FULLNAME='$fullname', DEPT='$dept', 
      GENDER='$gender'
      where EMPNO='$empno'";
  $rs2=mysqli_query($db2, $sql2);
  if ($rs2==true){
    echo "The update for $empno has been saved<br>";
    echo "Back to <a href='listingupdate.php'>listing</a>";
  }
  else{
    echo ("Query cannot be executed!<br>");
    echo ("SQL Error : ".mysqli_error($db2));
  }
}//end if NULL
?>