Add combobox in HTML form and select ,insert data using PHP

I am not getting your point. Where you want to add Combobox. You can add the select option for all subjects like this - 

<select name="name">
  <option value="A">item1</option>
  <option value="B">item2</option>
  <option value="n">item_n</option> 
</select> 

Select all subjects and display them in the list. 

<select name="subject">
  <option value="">your PHP code </option>
</select> 

Change the subject variable according to your created variable for the subject. 

Thank you for asking this question here. I am glad to solve your problem. You can add a checkbox as the subject input box. 

 echo "<input type='checkbox' name='sujects' value='".$row['subjects']."<br />";

Use select query and display the data inside the checkbox. It will help you insert data using the name subject. 

Comment me if the problem occurs.

Add Combobox in PHP. 

Try this code. It will help you to add Combobox to your website HTML form.

include_once('config.php');
$result = mysql_query($mysqli,"SELECT students FROM table_name") or die(mysql_error());
if (mysql_num_rows($result)!=0)

{
echo '<select name="drop_2" id="drop_2">
      <option value=" " selected="selected">Choose one</option>';
   while($drop_2 = mysql_fetch_array( $result ))
{
  echo '<option value="'.$drop_2['students'].'">'.$drop_2['students'].'</option>';
}
echo '</select>';

Change table name and column name. 

I solved your problem. You can add Combobox like this. 

Follow the steps - 

1. Add this code at the subject input place.

<?php 
$cser=mysqli_connect("localhost","root","","test") or die("connection failed:".mysqli_error());
$result = mysqli_query($cser,"SELECT pname FROM crud2") or die(mysql_error());
if (mysqli_num_rows($result)!=0)
{
echo 'Product Name : <select name="pname">
      <option value=" " selected="selected">Choose one</option>';
   while($drop_2 = mysqli_fetch_array( $result ))
{
  echo '<option value="'.$drop_2['pname'].'">'.$drop_2['pname'].'</option>';
}
echo '</select>';
}
?> 

2. Now change the test database to, your database or add your config file. 

2. Change the crud2 table name to your table name. 

3. Change pname to the students' column name. 

In this way, you can add Combobox in your website HTML form using PHP and Mysql database tables.

Benefits - 

1. Select data and display it in Combobox.

2. Insert data using select name="pname" . Change pname according to your column name.