Unknown column ‘siteurl’ in ‘where clause’ WPDB outside

option_name is type VARCHAR, iow. a string

Try:

$wpdb->get_var("SELECT option_value FROM wp_options WHERE option_name="siteurl"");

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)