How can someone submit a comment when my site has no comment field?

You could also use the hook pre_comment_on_post to exit early:

add_action( 'pre_comment_on_post', '_scalar_wp_die_handler' );

This will not change the database.

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