count number of all comments by a user on different (non-repeated) posts

Question

If you want to count the number of posts the user commented on, you can try:

global $wpdb;

$sql="SELECT COUNT( comment_ID ) FROM " . $wpdb->comments . '  
        WHERE user_id = %d 
        AND comment_approved = "1"
        AND comment_type NOT IN ("pingback", "trackback" )
        GROUP by comment_post_ID';

$count = $wpdb->get_var( $wpdb->prepare( $sql, $user->ID ) );

where we group by the post ID.