请帮忙解释一下，多表联查，小弟我看太不懂，谢啦

请帮忙解释一下，多表联查，我看太不懂，，谢啦

SQL code

select * from (select bookid,count(bookid) as degree from tb_borrow group by bookid) as borr join (select b.*,c.name as bookcasename,p.pubname,t.typename from tb_bookinfo b left join tb_bookcase c on b.bookcase=c.id join tb_publishing p on b.ISBN=p.ISBN join tb_booktype t on b.typeid=t.id where b.del=0) as book on borr.bookid=book.id order by borr.degree desc limit 10 

SQL code

select * from 
    (
        select bookid,count(bookid) as degree from tb_borrow group by bookid
    )
as borr 
join 
      (
         select b.*,c.name as bookcasename,p.pubname,t.typename from tb_bookinfo b left join tb_bookcase c on b.bookcase=c.id join tb_publishing p on b.ISBN=p.ISBN join tb_booktype t on b.typeid=t.id where b.del=0
      ) 
as book on borr.bookid=book.id order by borr.degree desc limit 10