SELECTuser.nickname,visitors.week_likesFROMuserJOINvisitorsON(user.id=visitors.user_id)WHERE(user.role>=0ANDvisitors.week_num=10ANDvisitors.week_likes>0AND(user.show_index!=-1ORuser.show_indexISNULL))ORDERBYvisitors.week_likesDESC,user.last_seenDESCLIMIT100user.id和visitors.id是主鍵，user.id與visitors.user_id對應。對visitors.user_id建立了索引，沒什么效果，在SQL語句和索引方面能怎樣優化？由于week_num和week_likes的區分度很低（=0AND(user.show_index!=-1ORuser.show_indexISNULL))aJOIN(SELECTvisitors.user_id,visitors.week_likesFROMvisitorsWHERE(visitors.week_num=10ANDvisitors.week_likes>0))bON(a.id=b.user_id)ORDERBYb.week_likesDESC,a.last_seenDESCLIMIT100;這句報錯，不知道原因在哪？還有其他什么方面可以優化的嗎？