語言目前總結：
表級子查詢
- 分組：
group by - 平均價格：
select round(avg(price）,2) from goods;
- 查詢所有價格大於平均價格的商品，併案價格降序排序：
select * from goods where price >(select round(avg(price),2)from goods) order by price desc;
- 查詢類型name 爲‘超極本’的商品名稱，價格：
select name,price from goods where cate_name ='超極本'
- 顯示商品的種類(distinct是區分的不重複內容）：select distinct cate_name from goods;
- 顯示商品種類方式2：
select cate_name from goods group by cate_name;
- 顯示每種類型的商品的平均價格：
select cate_name, max(price) as 最貴, min(price) as 最便宜，avg(price) as 平均價, count(*) as 總數量
avg(price) from goods
group by cate_name;
- 查詢每種類型中最貴的商品：
select *
from goods inner join
(select cate_name, max(price) as 最貴, min(price) as 最便宜，avg(price) as 平均價, count(*) as 總數量
avg(price) from goods
group by cate_name) as info on goodscate_name = info.cate_name and goods.price =info.最貴;
行級子查詢
= => in or => any
select * from goods where (cate_name,price) = in (select cate_name ,max(price) from goods group by cate_name);
創建商品分類表
create table if not exists goods_cates(id int unsigned primary key auto_increment, name varchar(40) not null);
- 查詢商品類別
insert into goods_cates(name) select distinct cate_name from goods;
- 將good表的brand_name轉化 select distinct cate_name from goods;
update tabel select colum =xx;
update goods as g inner join goods_cates as c on g.cate_name = c.name set g.cate_name = c.id;
- 更新字段名稱和數據類型
alter table goods change cate_name cate_id int unsigned not null;
待updat 10.30
