优化Oracle with全表扫描的问题
今天开发接了一个很BT的需求。
找一个人的所有好友，查询所有好友的所有作品，然后按照时间倒序排列,取若干记录，
然后关联作品评论表。
作品包括原唱表，翻唱表，伴奏表，视频表，博客表和照片表,
不同的作品类型还要关联不同的专辑表，最后还要关联用户表..
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结果就是这个SQL很长...
with
t1 as (select to_userid from friend_list f where f.userid=411602438),
t2 as (
select 'mc' as t,rid,createtime
from
(
select mc.rowid rid,mc.createtime from music_cover mc,t1 where mc.userid=t1.to_userid and mc.opus_stat >0 order by mc.createtime desc
) where rownum< 100
union all
select 'mo',rid,createtime
from
(
select mo.rowid rid,mo.createtime from music_original mo,t1 where mo.userid=t1.to_userid and mo.opus_stat >0 order by mo.createtime desc
) where rownum< 100
union all
select 'mv',rid,createtime
from
(
select mv.rowid rid,mv.createtime from music_video mv,t1 where mv.userid=t1.to_userid and mv.opus_stat >0 order by mv.createtime desc
) where rownum< 100
union all
select 'ma',rid,createtime
from
(
select ma.rowid rid,ma.createtime from music_accompany ma,t1 where ma.userid=t1.to_userid and ma.opus_stat >0 order by ma.createtime desc
) where rownum< 100
union all
select 'bl',rid,createtime
from
(
select bl.rowid rid,bl.createtime from blog_list bl,t1 where bl.userid=t1.to_userid and bl.opus_stat >0 order by bl.createtime desc
) where rownum< 100
union all
select 'pl',rid,createtime
from
(
select pl.rowid rid,pl.createtime from photo_list pl,t1 where pl.userid=t1.to_userid and pl.opus_stat >0 order by pl.createtime desc
) where rownum< 100
),
t3 as
(
select * from
(
select * from t2 order by createtime desc
)
where rownum<100
),
t4 as
(
select
t3.t,
decode(t3.t,
'mc',2,
'mo',2,
'mv',2,
'ma',2,
'pl',4,
'bl',5
) type_code,
mc.userid||mo.userid||mv.userid||ma.userid||bl.userid||pl.userid userid,
mc.file_url||mo.file_url||mv.file_url||ma.file_url||bl.file_url||pl.file_url file_url,
mc.opus_Name||mo.opus_Name||mv.opus_name||ma.opus_name||bl.opus_name||pl.opus_name opus_name,
mc.opus_id||mo.opus_id||mv.opus_id||ma.opus_id||bl.opus_id||pl.opus_id opus_id,
mc.createtime||mo.createtime||mv.createtime||ma.createtime||bl.createtime||pl.createtime createtime,
mv.opus_desc||mo.opus_desc||mc.opus_desc||ma.opus_desc||bl.opus_desc||pl.opus_desc opus_desc,
mv.album_id||mo.album_id||mc.album_id||ma.album_id||bl.album_id||pl.album_id album_id,
mv.visit_num||mo.visit_num||mc.visit_num||ma.visit_num||bl.visit_num||pl.visit_num visit_num
from t3
left join music_cover mc on(t3.rid=mc.rowid)
left join music_original mo on(t3.rid=mo.rowid)
left join music_video mv on(t3.rid=mv.rowid)
left join music_accompany ma on(t3.rid=ma.rowid)
left join blog_list bl on(t3.rid=bl.rowid)
left join photo_list pl on(t3.rid=pl.rowid)
)
select /*+ ordered use_nl(t4,base) */
base.nickname,
decode(t4.type_code,
2,(select al.album_name from music_album al where al.album_id=t4.album_id),
4,(select al.album_name from photo_album al where al.album_id=t4.album_id),
5,(select al.album_name from blog_album al where al.album_id=t4.album_id)
) album_name,
(select count(*) from user_comment com where com.typeid=t4.type_code and t4.opus_id=com.to_id and status=1) commentTotal,
t4.*
from t4,mvbox_user.user_baseinfo base where base.userid=t4.userid;
创建索引消除排序
create index inx_music_cover on music_cover(userid,opus_stat,operTime);
create index inx_music_original on music_original(userid,opus_stat,operTime);
create index inx_music_video on music_video(userid,opus_stat,operTime);
create index inx_music_accompany on music_accompany(userid,opus_stat,operTime);
create index inx_blog_list on blog_list(userid,opus_stat,operTime);
create index inx_photo_list on photo_list(userid,opus_stat,operTime);
create index inx_user_comment on user_comment(to_id,typeid,status);
用户表比较大，是一个有900w记录的分区表。查看执行计划，都符合预期，只是最后关联用户表的时候，使用了全表扫描，直接导致这个SQL执行了20s左右。但是用户表的关联字段明明已经创建了索引。。