Question

I have a similiar class with a lot of methods, but getData() only returns the value of the $column parameter.

private $db;

function __construct()
{
    $this->db = new PDO('sqlite:\db');
}

public function getData($rowid, $column)
{
    $st = $this->db->prepare('SELECT ? FROM tbl WHERE rowid=?');
    $st->bindParam(1, $column, PDO::PARAM_STR);
    $st->bindParam(2, $rowid, PDO::PARAM_INT);
    if ($st->execute())
        return $st->fetchColumn();
    else
        return false;
}

Every other parts of the class and the left out half of getData() works. What’s the problem here?

Answer 1

bindParam is used to bind parameters, not identifiers. The value you bind there will be expanded as:

SELECT 'some_value' FROM tbl WHERE rowid='some_other_value';

…therefore equivalent to:

SELECT 'some_value';

You should only use parameters for actual parameters:

$this->db->prepare('SELECT '.$column.' FROM tbl WHERE rowid=?');

If your column is user-supplied and you want to escape it, use the proper escaping function. In this case, it’s SQLite3::escapeString():

$column = SQLite3::escapeString($column);
$this->db->prepare('SELECT '.$column.' FROM tbl WHERE rowid=?');

If the column is not user-supplied, you don’t really have to escape it.