LeetCode 【困难】数据库-第1159：市场分析|| yes -no （Case when ‘分类’ ）=if的使用

题目

表结构

数据

结果

解答：

1.连接表，查看按日期顺序卖出的产品都有哪些

select orders.seller_id,
			 orders.order_date,
			 orders.item_id,
			 items.item_id item_ids,
			 item_brand,row_number() over(partition by seller_id order by order_date) as rk
from Orders 
join Items
on Orders.item_id=Items.item_id

1.1 看第二件

select *
from(

select orders.seller_id,
			 orders.order_date,
			 orders.item_id,
			 items.item_id item_ids,
			 item_brand,row_number() over(partition by seller_id order by order_date) as rk
from Orders 
join Items
on Orders.item_id=Items.item_id

) a
where rk=2

2.查item_brand和卖家最爱的favorite_brand 是否相同

select * ,
		case when item_brand = favorite_brand then 'yes' # 第一种方法，使用case when then else end
		else 'no' end 'love' ,
if(favorite_brand=item_brand ,'yes','no') # 第二种方法，使用if函数
from users,items

3.连接1.2表结果

select Users.user_id as seller_id,
			if(favorite_brand=item_brand,'yes','no') as 2nd_item_fav_brand ,
			case when item_brand=favorite_brand then 'yes' 
					 else 'no' end '2nd_item_fav_brands'
from Users 
left join 
(
select *
from(

select orders.seller_id,
			 orders.order_date,
			 orders.item_id,
			 items.item_id item_ids,
			 item_brand,row_number() over(partition by seller_id order by order_date) as rk
from Orders 
join Items
on Orders.item_id=Items.item_id

) a
where rk=2
) b
on Users.user_id =b.seller_id