Кто нибудь объяснит что хотел разработчик - MySQL

public function Friends_Updates($uid, $lastid, $lastmid, $lastsid) {
  $moresharequery = "";
  if ($lastsid) {
       $moresharequery = " and S.share_id > '" . $lastsid . "' ";
   }
 
  /* More Button*/
  $morequery="";
  if($lastid) {
      //build up the query
      $morequery=" and M.msg_id<'".$lastid."' ";
   }
   if($lastmid) {
      //build up the query
      $morequery=" and M.msg_id>'".$lastmid."' ";
   }
    $data = null;
    /*More Button End*/
    $v=mysqli_query($this->db,"SELECT share_id FROM message_share") or die(mysqli_error($this->db));
    if(mysqli_num_rows($v)) {
       //The query to select friend messages
       $query=mysqli_query($this->db,"(SELECT DISTINCT 
             M.msg_id,
             M.uid_fk,
             M.shared_uid_fk,
             M.shared_msg_id_fk,
             M.last_shared_uid_fk,
             M.message,
             M.hide_show_comment,
             M.hide_show_share,
             M.postPrivacy,
             M.lovedPost,
             M.hashTag,
             M.share_count,
             S.created,
             M.like_count,
             M.comment_count,
             U.username,
             M.uploads,
             S.uid_fk AS share_uid,
             S.ouid_fk AS share_ouid
             FROM 
             messages M
             JOIN message_share S ON M.msg_id = S.msg_id_fk
             JOIN friends F ON F.friend_two = S.uid_fk OR S.uid_fk = '$uid'
             JOIN users U ON S.ouid_fk = U.uid
             WHERE 
             F.friend_one='$uid'
             AND U.uid != F.friend_one 
             AND U.status='1'
             AND F.role='fri'
             $moresharequery
             )
             UNION
             (SELECT DISTINCT 
             M.msg_id,
             M.uid_fk,
             M.shared_uid_fk,
             M.shared_msg_id_fk,
             M.last_shared_uid_fk,
             M.message,
             M.hide_show_comment,
             M.postPrivacy,
             M.hide_show_share,
             M.lovedPost,
             M.hashTag,
             M.share_count,
             M.created,
             M.like_count,
             M.comment_count,
             U.username,
             M.uploads,
             '0' AS share_uid,
             '0' AS share_ouid
             FROM 
              messages M 
              JOIN users U ON M.uid_fk = U.uid
              JOIN friends F ON M.uid_fk = F.friend_two
             WHERE 
              F.friend_one='$uid'
              AND U.status='1'
            $morequery ) order by created desc limit " .$this->perpage) or die(mysqli_error($this->db)); 
       } else {    
          $query = mysqli_query($this->db,"SELECT DISTINCT M.msg_id, M.uid_fk,M.shared_uid_fk,M.shared_msg_id_fk,M.last_shared_uid_fk, M.message,M.hide_show_comment,M.postPrivacy,M.hide_show_share,M.lovedPost,M.hashTag,M.like_count,M.comment_count, M.created,U.username,M.uploads FROM messages M, users U, friends F  WHERE U.status='1' AND M.uid_fk=U.uid AND  M.uid_fk = F.friend_two AND F.friend_one='$uid' $morequery order by M.msg_id desc limit " .$this->perpage) or die(mysqli_error($this->db));
       }
        //Store the result
        while($row=mysqli_fetch_array($query)) {
            // Store the result into array
            $data[]=$row;
            }
             if(!empty($data)) {
               // Store the result into array
               return $data;
            }  
}