class DatabaseConnection {

    protected $db_user = '';
    protected $db_pass = '';
    protected $db_dsn = 'mysql:host=localhost;dbname=';
    protected $options = array(
        PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8',
        PDO::ATTR_ERRMODE => PDO::ERRMODE_WARNING,
    );

    public function dbconnect(){
        try {
            $db = new PDO($this->db_dsn, $this->db_user, $this->db_pass, $this->options);
        }
        catch (PDOException $e) {
            echo 'Connection failed: ' . $e->getMessage();
            exit;
        }
            return $db;
        }
    }

class dbTools {

    private $db;
    private $verifiedTable;
    private $verifiedColumn;
    private $verifiedItemId;

    function __construct() {
        $this->db = new DatabaseConnection();
        $this->db = $this->db->dbconnect();
    }

    public function validateValues($table, $column, $itemId) {
        // Verify that table exists
        $verifiedTable = $this->verifyTable($table);
        $this->verifiedTable = $verifiedTable;

        // Verify that column exists
        $verifiedColumn = $this->verifyColumn($column, $this->verifiedTable);
        $this->verifiedColumn = $verifiedColumn;

        // Verify that id exists
        $verifiedItemId = $this->verifyItemId($this->verifiedTable, $itemId);
        $this->verifiedItemId = $verifiedItemId;
    }

    private function verifyTable($table) {
        $result = $this->db->query("show tables");
        $final = $result->fetchAll(PDO::FETCH_COLUMN);

        if(in_array($table, $final)) {
            $verifiedTable = $table;
        } else {
            throw new exception('Table doesn´t exists');
        }
        return $verifiedTable;
    }

    private function verifyColumn($column, $verifiedTable) {
        $result = $this->db->query('SHOW COLUMNS FROM '.$verifiedTable.'');
        $columns = $result->fetchAll(PDO::FETCH_COLUMN);

        if(in_array($column, $columns)) {
            $verifiedColumn = $column;
        } else {
            throw new exception('Column doesn´t exist');
        }
        return $verifiedColumn;
    }

    private function verifyItemId($verifiedTable, $itemId) {
        $result = $this->db->query('SELECT id FROM '.$verifiedTable.'');
        $ids = $result->fetchAll(PDO::FETCH_COLUMN);

        if(in_array($itemId, $ids)) {
            $verifiedItemId = $itemId;
        } else {
            throw new exception('Id doesn´t exist');
        }
        return $verifiedItemId;
    }

    public function getItem() {
        $statement = 'SELECT '.$this->verifiedColumn.' FROM '.$this->verifiedTable.' WHERE id = :id';
        $query = $this->db->prepare($statement);
        $query->bindParam(':id', $this->verifiedItemId);
        $query->execute();
        $row = $query->fetchColumn();
        return $row;
    }
}

$dbTools = new dbTools();
$dbTools->validateValues('table','column', 'id');
echo $dbTools->getItem();