5.having,limit,orderby使用详解

having详解

having关键字在select 和where 之后

where 和select 称为查询

having是查询结果后的筛选

如

查询商店所有商品卖价与商城相比能省200以上的商品.

select goods_id,goods_name,shop_price - goods_price as sheng having sheng > 200;

如图

同上题,只查询第个栏目下比市场低200元以上的商品

select goods_id,goods_chat,goods_name,shop_price - goods_price as sheng where goods_chat = 3 having sheng >200;

查询积压货款超过2W点栏目。以及该栏目积压的货款

select cat_id,sum(goods_price * goods_num) as jiya from goods group by cat_id having jiya >20000;

题目如上图

select 姓名,科目, sum(分数< 60 ) as bujigenum,avg(分数) as pjfen from stu group by 姓名 having bujigenum >=2;

不用左链接，不用子查询写法

order by排序

order by 可以按多字段排序,order by 列1 [desc\asc],列2 [desc/asc]

limit 限制几行

limit放在语句最后，起到限制条目的作用

limit [offset,]N

offset:偏移量

N:取出条目

offset:如果不写，则相当于 limit 0,N