Invalid statement / prepare while doing SELECT on class

What's wrong with this class?

<?php
class myClass {
  private $dbServer  = 'localhost';
  private $dbUser    = 'db_name';
  private $dbPass    = 'db_pass';
  private $dbName    = 'db_name';

  var $error  = NULL;
  var $db;

  function connect()
  {
    // improved by http://stackoverflow.com/users/618622/bv202
    try
    {
      $this->db = new PDO('mysql:host=' . $this->dbServer . ';dbname=' . $this->dbName, $this->dbUser, $this-开发者_运维问答>dbPass);
      $this->db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
      return (!$this->db) ? FALSE : TRUE;
      $this->db = NULL;
    }
    catch (PDOException $e)
    {
      print "Error!: " . $e->getMessage() . "<br/>";
      die();
    }
  }

  function columns($table)
  {
    if(!$this->connect()) $this->error =  'Error connecting/creating PDO.';
    else
    {
      $columnsTable = $this->db->prepare("DESCRIBE :_table"); // here points out the error
      if(!$columnsTable) $this->error = 'Invalid statement';
      else
      {
        $columnsTable->bindParam(':_table', $table);
        if(!$columnsTable->execute()) $this->error = 'Error while executing statement.';
        else
        {
          $columns = $columnsTable->fetchAll();
          if(!$columns) $this->error = 'Invalid fetch.';
          else
          {
            $columnsTable->closeCursor();
            foreach($columns as $column=>$columnData)
            {
              $results[] = $columnData['COLUMN_NAME'];
            }
          }
        }
        $columnsTable = NULL;
      }
    }
    return !empty($this->error) ? $this->error : $results;
  }

}

$control = new myClass;
$content = $control->columns('customers');
var_dump($content);
?>

Outputs:

string(17) "Invalid statement"

I tested the SQL directly on MySQL without errors.

MySQL version: 5.0.92

PHP version: 5.2.11

With Prepared statements, you cannot use parameters just anywhere in any possible kind of query : it's not like a "put this into a string" : prepared statements depend on the server.

I suppose MySQL doesn't accept a parameter in a describe query -- which explains the error.

You'll have to not use prepared statements, for this kind of query.

Quoting MySQL's documentation :

Parameter markers can be used only where data values should appear, not for SQL keywords, identifiers, and so forth.

In your case, you are trying to use a parameter marker for an identifier (a table's name) -- which is not supported.