sql - 如何根据字母顺序仅保留 1 个结果以与 SQL 查询保持一致？

Question

该问题要求以每个国家/地区的客户购买商品金额最高的城市为例。基本上，有些城市的商品数量相同，但我们只保留第一个按字母顺序排列。结果仅包含国家名称、商品数量最多的城市及其商品总和。

表架构：

Country table:
country_name
city_name

Goods table:
city_name
user_id
number_of_goods

我的查询结果：

France            Paris        85
Germany           Berlin       100
Germany           Frankfurt    100
Germany           Luxembourg   100
Netherlands       Amsterdam    75
Spain             Barcelona    93

正确的结果应该是：

France            Paris        85
Germany           Berlin       100
Netherlands       Amsterdam    75
Spain             Barcelona    93

Answer 1

您可以使用row_number()：

select t.*
from (select t.*, row_number() over (partition by country order by city) as seq,
             max(no_goods) over (partition by country) as max_good
      from table t
     ) t
where seq = 1;

Answer 2

min()对 city 和max()no_of_goods使用聚合函数。

select t1.country, t1.no_of_goods, min(t2.city) as city 
from
(select country,  max(no_of_goods) as no_of_goods from tableA
group by country) t1
left join tableA t2 on t2.no_of_goods = t1.no_of_goods and t1.country = t2.country
group by t1.country, t1.no_of_goods

见dbfiddle。

Answer 3

基本上，有些城市的商品数量相同，但我们只保留第一个按字母顺序排列。

根据您的样本数据，一个国家的所有城市似乎都有相同的number_of_goods. 如果是这样，您可以只使用聚合：

select c.country, min(c.city_name), max(number_of_goods)
from countries c join
     goods g
     on c.city_name = g.city_name
group by c.country;