$res = \db('BooksInfo')->alias('bi')->join('user u','bi.user_id = u.uid')->field('info,state,yy_time,uid,sum(bi.books_price) as books_price')->group('yy_time,uid')->order('books_id desc')->paginate($_GET['limit']);
field：必須出現(xiàn)的字段方椎，用‘孔厉，’隔開
group：需要合并的條件字段
sum(bi.books_price) as books_price：sum()集合 as books_price別名填寫你要集合的字段
