order by

4、order by
（1）order by price         //默认升序排列
（2）order by price desc //降序排列
（3）order by price asc  //升序排列，与默认一样
（4）order by rand()      //随机排列，效率不高
    #按栏目号升序排列，每个栏目下的商品价格降序排列
    select * from goods where cat_id !=2 order by cat_id,price desc;