有没有办法从SQL查询返回绑定结果？

I have a SQL table for a menu system. It has "id" as an index, a "display" field and a "parent" field. These are the data:

id, display, parent
1, File, 0
2, View, 0
3, Window, 0
4, Open, 1
5, Save, 1
6, Export, 1
7, Export to Image, 6
8, Export to PDF, 6
9, JPEG, 7
10, PNG, 7

I wanted to have a function to return the menu hierarchy in an HTML select format. The desired output would look like this:

<option value='1'>File</option>
<option value='4'>-- Open</option>
<option value='5'>-- Save</option>
<option value='6'>-- Export</option>
<option value='7'>---- Export to Image</option>
<option value='9'>------ JPEG</option>
<option value='10'>------ PNG</option>
<option value='8'>---- Export to PDF</option>
<option value='2'>View</option>
<option value='3'>Window</option>

This is the function I came up with:

function SelectPage($pdo, $default = "", $depth = 0, $id = 0, $opts = "") {
  $sql = $pdo->prepare("SELECT id,display FROM pages WHERE parent = ?");
  $sql->execute(array($id));
  while ($row = $sql->fetch(PDO::FETCH_ASSOC)) {
    $opts .= "<option value='{$row["id"]}'>";
    $opts .= trim(str_repeat("--", $depth) . " ");
    $opts .= "{$row["display"]}</option>";
    $tmp = SelectPage($pdo, $default, ($depth + 1), $row["id"], $opts);
    $opts = $tmp;
  }
  return $opts;
}

It works, but I have doubts as to how efficient that is. I was wondering if there was a way to make a SQL query that returns them already in the correct order so that I could avoid doing looping calls to itself?

Dont use recursive with your sql statement. In one query take all categories to array like this:

$categories = array( 
   array(
     'id' => 1,
     'name' => 'File',
     'parent' => 0
   ),
   ... etc.
);

next use this simple function. You can modify if You want.

function isSubCategory( $id, $cats )
{
    foreach( $cats as $cat )
    {
        if( $id != $cat['id'] && $id == $cat['parent'] )
         return true;
    }
    return false;
} 
echo '<select>';
function getRecursiveTree( $parent, $cats, $level = -1 )
{
  $separator = '-';
  foreach( $cats as $i => $cat )
    {
      if( $cat['parent'] == $parent ) 
        {
          $level++;
      if( isSubCategory( $cat['id'], $cats ) )
      {
        echo '<option value="',$cat['id'],'">', str_repeat( $separator, $level ) , $cat['name'],'</option>' . PHP_EOL;
        getRecursiveTree( $cat['id'], $cats, $level );                        
      }
      else
      {
        echo '<option value="',$cat['id'],'">', str_repeat( $separator, $level ) , $cat['name'],'</option>' . PHP_EOL;
      }
      $level--;        
    } 
    }   
}

echo ( getRecursiveTree( 0, $k ) );
    echo '</select>';