Very strange database result

Hello!
I have a code that fetches settings from the DB but instead of returning a value it returns key name.

The code:

PHP Code:

public function getValue($key){
        $CI =& get_instance();
        $query = $CI->db->query('SELECT ? FROM settings', array($key));
        $row=$query->result_array()[0];
        var_dump($row);
        //return $row[$key];
    } 


The output:

Code:

array(1) { ["max_problems_in_selector"]=> string(24) "max_problems_in_selector" }

The table:
   

So what $key are you specifying?

Use last_query() to check that you are getting a correct SQL query. Run that one in phpmyadmin and see if that give you the correct results.