Leave default option value empty in html select

问题

I have an html select that is populated with DATA from a query using a foreach loop. It looks something like this

$client = $wpdb->get_results("SELECT string FROM `file` WHERE 
`code` = 002 AND `status` = 2");

echo 'Filter by client: ';
  echo '<select name="client_list">';
  foreach ($client as $key => $row) {
    $value = $row->string;
    echo 
  '<option value='.$value.'>'
  .$value. '</option>';
  }
  $client = $_GET['client_list'];
  echo '</select>';

It serves as a filter to display data based on the selected option value. The table that it filters looks somehting like this

   |client  | file              | 
   |------  |-------------------|
   |client1 | file00000         |
   |client2 | file00002         |

Now I want to make the first option value (the default value) of the html empty. How do I do this?

回答1:

you can use this

      $client = $wpdb->get_results("SELECT string FROM `file` WHERE 
     `code` = 002 AND `status` = 2");

    echo 'Filter by client: ';
    echo '<select name="client_list"><option value=""></option>';
    foreach ($client as $key => $row) {
        $value = $row->string;
        echo 
       '<option value='.$value.'>'
        .$value. '</option>';
    }
    $client = $_GET['client_list'];
    echo '</select>';

回答2:

Add an empty option first:

echo '<select name="client_list"><option value=""></option>';

on submit if client_list is empty you know someone didn't choose anything.

来源：https://stackoverflow.com/questions/46582289/leave-default-option-value-empty-in-html-select