some combobox reset each other after selected - php

Question

I have some combobox with onchange event, and they're reset each other when selected the orther one of them, does any suggest how to retain the value on the page? this my script :
<form method="POST" name="form1" action="<?php $_SERVER['PHP_SELF'];?>">
<table border="0">
<tr>
<td colspan="6"></td>
</tr>
<tr>
<td>
<select name="select_petugas1" style="width:18px;" onchange="this.form.submit('select_petugas1');"> //first combobox
<option></option>
<?php include 'dbconn.php';
$sql_peg1="SELECT * FROM users"; $result_peg1=$conn->query($sql_peg1);
while( $row_peg1=$result_peg1->fetch_assoc() ){
echo "<option>".$row_peg1['nama']."</option>";
}
?>
</select>
</td>
<td>
<?php
if(isset($_POST['select_petugas1'])){
$select_petugas1=$_POST['select_petugas1'];
echo "<input type='text' name='select_petugas1' value='".$select_petugas1."'>"; // Throw 1st result into the text box
$sql_NIP1="SELECT NIP FROM users WHERE nama='$select_petugas1'";
$result_NIP1=$conn->query($sql_NIP1);
$row_NIP1=$result_NIP1->fetch_assoc();
$NIP1=$row_NIP1['NIP'];
?>
</td>
<td> NIP</td>
<td>:</td>
<td><input type="text" name='NIP1' value="<?php echo $NIP1; ?>"></td>
</tr> <!-- child of first result -->
<tr>
<td colspan="5" bgcolor="blue"></td>
</tr>
<tr>
<td>
<select name="peg_2" style="width:18px;" onchange="submit(this)"><!--2nd combobox-->
<option></option>
<?php
$sql_peg2="SELECT nama FROM users";
$result_peg2=$conn->query( $sql_peg2 );
while ($row_peg2=$result_peg2->fetch_assoc()){
echo "<option value='".$row_peg2['nama']."'>".$row_peg2['nama']."</option>";
}
?>
</select>
</td>
<td>
<?php
if( isset($_POST['peg_2']) ){
$peg_2=$_POST['peg_2'];
echo "<input type='text' name='peg2' value='".$peg_2."'>"; // 2nd result throw into 2nd texbox
$sql_NIP2="SELECT NIP FROM users WHERE nama='$peg_2'";
$result_NIP2=$conn->query($sql_NIP2);
$row_NIP2=$result_NIP2->fetch_assoc();
?>
</td>
<td> NIP</td>
<td>:</td>
<td><input type='text' name='NIP2' value="<?php echo $row_NIP2['NIP'];?>"> <!--2nd child of result-->
<?php
}
}
if(isset($_POST['NIP2'])){
$NIP2=$_POST['NIP2'];
echo "<br /> NIP2 :".$NIP2."<br />";
}
mysqli_close($conn);
?>
</td>
</tr>
</table>
</form>
<form method="POST" name="wilayah" id="wilayah" action="<?php $_SERVER['PHP_SELF'];?>">
<table border="1">
<tr>
<td>
<select name="select_provinsi" onchange="submit(this)" style="width:18;">
<option selected>PROVINSI</option>
<?php
include 'dbconn.php';
$sql_prov="SELECT * FROM wilayah GROUP BY provinsi";
$result_prov=$conn->query($sql_prov);
echo "";
while($row_prov=$result_prov->fetch_assoc()){
$provinsi=$row_prov['provinsi'];
echo "<option value='".$provinsi."'>".$provinsi."</option>";
}
?>
</select>
<?php
if(isset($_POST['select_provinsi'])){
$select_provinsi=$_POST['select_provinsi'];
echo "
<input type='text' name='select_provinsi' value='".$select_provinsi."' placeholder='PROVINSI'>
</td>
</tr>";
$sql_kabkota="SELECT * FROM wilayah WHERE provinsi='$select_provinsi' GROUP BY kab_kota";
$result_kabkota=$conn->query($sql_kabkota);
?>
<tr>
<td>
<select name="select_kabkota" style="width:18px;" onchange="submit(this)"><option>KAB/KOTA</option>
<?php
while($row_kabkota=$result_kabkota->fetch_assoc()){
echo "<option>".$row_kabkota['kab_kota']."</option>";
}
?>
</select>
<?php
}
if(isset($_POST['select_kabkota'])){
$select_kabkota=$_POST['select_kabkota'];
?>
<input type="text" name="kab_kota" value="<?php echo $select_kabkota;?>">
<?php
}
mysqli_close($conn);
?>
</td>
</tr>
</table>
</form>
hope any suggestion for resolved of my problem with them,,

Answer 1

onchange="submit(this)" means that you want to submit the form when the value of the combobox changes. So, when the form is sent, the page reloads and you get the default value of your form.
To restore the chosen value, I would do something like :
<select name="select_kabkota" style="width:18px;" onchange="submit(this)">
<option>KAB/KOTA</option>
<?php
if(isset($_POST['select_kabkota']))
$select_kabkota=$_POST['select_kabkota'];
while($row_kabkota=$result_kabkota->fetch_assoc())
{
$selected = $select_kabkota == $row_kabkota['kab_kota'] ? 'selected="selected"' : '';
echo "<option ".$selected." >".$row_kabkota['kab_kota']."</option>";
}
?>
</select>