select articleno, title, regdate, hit, name, attachfilenum, commentnum

from (select rownum r, a.* 

from (select a.articleno, a.title, a.regdate, a.hit, m.name, count(distinct(c.commentno)) commentnum

from article a, attachfile f, comments c, membership m

where a.articleno = f.articleno(+)

and a.articleno = c.articleno(+)

and a.id = m.memberid(+)

and a.boardcd = ?

group by a.articleno, a.title, a.regdate, a.hit, m.name order by articleno desc 

     ) a

      )

where r between ? and ?

이게 쿼리문 하나인데요 ;;

다른 건 다 알겠는데 (+) 이 기호가 의미하는 게 뭔지 모르겠어요 

알려주시면 감사하겠습니다