新手图书馆系统,问个有关问题

新手图书馆系统,问个问题
$readerid=$info[id];
$sql1=mysql_query("select r.*,borr.borrowTime,borr.backTime,book.bookname,book.price,pub.pubname,bc.name as bookcase from tb_borrow as borr join tb_bookinfo as book on book.id=borr.bookid join tb_publishing as pub on book.ISBN=pub.ISBN join tb_bookcase as bc on book.bookcase=bc.id join tb_reader as r on borr.readerid=r.id where borr.readerid='$readerid' and borr.ifback=0");
//$sql=mysql_query("select t.days from tb_bookinfo b left join tb_booktype t on b.typeid=t.id where b.barcode='$barcode'");
$info1=mysql_fetch_array($sql1);
$borrowNumber=mysql_num_rows($sql1); //获取结果集中行的数目
do{
?>

这段代码里面的sql操作是什么意思?这是一个图书馆信息管理系统,而且还没办法实现借书的功能,求找bug
------解决方案--------------------
通过 $readerid 查找这个id的借书情况
展示 借书信息 书本信息等等