两条速度相差1350倍儿的sql语句

select *from RESOURCES where  RES_STATUS = 1 and PLATFORM_FLAG=1 and  RES_ID in    (select RES_ID from DOWNLOADRECORDS where DOWNLOADRECORDS_TIME > DATE_SUB(now(),INTERVAL 7 DAY)     group by RES_ID order by COUNT(*) desc ) limit 1, 10;

?这条语句查处结果需要20250毫秒

  select bb.* from (select * from DOWNLOADRECORDS where DOWNLOADRECORDS_TIME > DATE_SUB(now(),INTERVAL 7 DAY) group by RES_ID order by COUNT(*) desc limit 1,10) as aa,RESOURCES as bb  where aa.RES_ID=bb.RES_ID  and bb.RES_STATUS = 1 and bb.PLATFORM_FLAG=1;

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这条语句只需要15毫秒

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相同的环境下，查出相同的结果速度相差1000倍