Get the selected dropdown related value into the text box - php

Question

I want to generate the salary after user selects the designation dropdown value from the database.
my db strucuture is as follows:
employee:
emp_id dep_id
1 1
2 1
designation:
dep_id des_name salary
1 accountant 20000
This is my html code:
<div class="form-group">
<label class="control-label col-lg-2" for="initial">Designation :</label>
<div class="col-lg-3">
<select class="form-control input-sm" name="classification" id="classification" onchange="changeValue();">
<?php while($row3 = mysqli_fetch_array($result3)):; ?>
<option><?php echo $row3[2]; ?></option>
<?php endwhile; ?>
</select>
<span class="error_form" id="classification_error_message"></span>
</div>
<label class="control-label col-lg-2" for="basicSalary">Basic Salary :</label>
<div class="col-lg-3">
<input type="text" class="form-control input-sm" name="basicSalary" id="basicSalary" placeholder="0.00">
</div>
</div>

Answer 1

You can do this by using this code butt this code from php codeigniter. Now u can changing it according to your requirements.
<div class="item form-group">
<label class="control-label col-md-3 col-sm-3 col-xs-12" for="name">select Categories <span class="required">*</span>
</label>
<div class="col-md-6 col-sm-6 col-xs-12">
<select class="form-control" name="cat" id="catogires">
<!-- <option value="">Select categories</option>-->
<?php
$data=$this->Product_Model->cat_select();
foreach($data as $row)
{ ?>
<option <?php if ($product->cat_id==$row->cat_id) echo "selected='selected'"; ?> value="<?php echo $row->cat_id?>"><?php echo $row->cat_name;?></option>
<?php
}
?>
</select>
</div>
</div>