2- SQL语句的强化

    查询类型cate_name为 '超极本' 的商品名称、价格

select name,price from goods where cate_name = '超级本';

    显示商品的种类

select cate_name from goods group by cate_name;

    求所有电脑产品的平均价格,并且保留两位小数

select round(avg(price),2) as avg_price from goods;

    显示每种商品的平均价格

select cate_name,avg(price) from goods group by cate_name;

    查询每种类型的商品中 最贵、最便宜、平均价、数量

select cate_name,max(price),min(price),avg(price),count(*) from goods group by cate_name;

    查询所有价格大于平均价格的商品，并且按价格降序排序

select id,name,price from goods 
where price > (select round(avg(price),2) as avg_price from goods) 
order by price desc;

    查询每种类型中最贵的电脑信息
select g.name,g.cate_name,g.price from (select cate_name,max(price) as max_price from goods group by cate_name) as g_new left join goods as g on g_new.cate_name=g.cate_name and g_new.max_price=g.price;

insert into goods values(0,'xiatian','笔记本','夏天','4999',default,default);

select g.name,g.cate_name,g.price from (select cate_name,max(price) as max_price from goods group by cate_name) as g_new left join goods as g on g_new.cate_name=g.cate_name and g_new.max_price=g.price order by g.cate_name;

查询所有价格大于平均价格的商品，并且按价格降序排序

select id,name,price from goods 
where price > (select round(avg(price),2) as avg_price from goods) #括号内的sql语句结尾没有分号;
order by price desc;