查询支持嵌套使用
查询各学生的语文、数学、英语的成绩
select sname, (select sco.score from scores sco inner join subjects sub on sco.subid=sub.id where sub.stitle='语文' and stuid=stu.id) as 语文, (select sco.score from scores sco inner join subjects sub on sco.subid=sub.id where sub.stitle='数学' and stuid=stu.id) as 数学, (select sco.score from scores sco inner join subjects sub on sco.subid=sub.id where sub.stitle='英语' and stuid=stu.id) as 英语 from students stu;