这条SQL语句不懂，能帮我解释下吗？
“select shop_action.actionid,shop_action.bookid,shop_action.bookcount,shop_action.zonger,shop_books.bookname,shop_action.shjiaid,shop_books.shichangjia,shop_books.huiyuanjia,shop_books.vipjia from shop_books inner join shop_action on shop_books.bookid=shop_action.bookid where shop_action.username='"&username&"' and shop_action.zhuangtai=7”