摘要：
select*fromscwhere(selectcount(*)fromscsc2wheresc2.score>sc.scoreandsc2.class=sc.class)<=2orderbysc.class,sc.scoredesc;select*fromschaving(selectcount(*)fromsct1wheret1.class=sc.classandt1.score>=sc.score)<=3;select*fromscwhereexists(selectcount(*)fromscsc2wheresc2.score>sc.scoreandsc 阅读全文