Question

含视图的SQL语句求解析

$sql=mysqli_query($conn,"select * from (select bookid,count(bookid)as degreefrom tb_borrow group by bookid) as borr join (select b.*,c.name as bookcasename,p.pubname,t.typenamefrom bookinfo b left join tb_bookcase c on b.bookcase=c.id join tb_publishing pon b.ISBN=p.ISBN join tb_booktype t on b.typeid=t.id where b.del=0) as book onborr.bookid=book.id order by borr.degree desc limit 10")

这一段查询语句怎么理解啊？
谢谢。跪求大神们指导~

Answer 1

/*帮你把语句排了下序，层次显得明显一点，也简单的注释下（主要是也不清楚你每张表以及字段各代表什么意思），不懂的追问*/

select *
  from (select bookid, count(bookid) as degree
          from tb_borrow
         group by bookid) as borr    --统计tb_borrow表中bookid各有多少条
  join (select b.*,c.name as bookcasename,p.pubname,t.typename 
        from bookinfo b                        --基础表bookinfo 
        left join tb_bookcase c on b.bookcase = c.id --左链接tb_bookcase
        join tb_publishing p on b.ISBN = p.ISBN  --内链接tb_publishing
        join tb_booktype t on b.typeid = t.id    --内链接tb_booktype
        where b.del = 0) as book
    on borr.bookid = book.id          --外层内链接两张中间表
 order by borr.degree desc limit 10  --按照borr表中degree从大到小排序，取前面10条