根据处理方式不同：

select a.*,if(@tmp=CONCAT(r_content,r_userid),@rownum:=@rownum+1,@rownum:=1) as rownum,@tmp:=CONCAT(r_content,r_userid) from (

select a.* from reviews a INNER JOIN

  (select r_content,r_userid,count(*) from reviews     GROUP BY r_content,r_userid having count(*)>1 ) b

 on a.r_content=b.r_content and a.r_userid=b.r_userid ) a,(select @rownum:=0,@tmp:='') b 

delete from xxx where r_id in 

或者

 select GROUP_CONCAT(r_id) as ids,r_content,r_userid,count(*) from reviews GROUP BY r_content,r_userid

HAVING count(*)>1