将 SQL 子查询转换为 Peewee ORM

Question

我有一个类似于Translate SQLite query, with subquery, into Peewee statement 和Can peewee nest SELECT queries such that the outer query selects on an aggregate of the inner query? 的问题。

我试图生成的结果是：给定一个包含(type, variety, price) 行的fruit 表，找出每种水果中最便宜的品种。 http://www.xaprb.com/blog/2006/12/07/how-to-select-the-firstleastmax-row-per-group-in-sql/ 描述了几个有效的解决方案：

select f.type, f.variety, f.price
from (
   select type, min(price) as minprice
   from fruits group by type
) as x inner join fruits as f on f.type = x.type and f.price = x.minprice;

或者：

select type, variety, price
from fruits
where price = (select min(price) from fruits as f where f.type = fruits.type);

我如何对其中一个或两个进行 Peewee-ify？

Answer 1

抄袭http://charlesleifer.com/blog/techniques-for-querying-lists-of-objects-and-determining-the-top-related-item/，我有：

subquery = (Fruits
            .select(
                Fruits.type.alias('type'),
                fn.Min(Fruits.price).alias('min'))
            .group_by(Fruits.type)
            .alias('subquery'))

query = (Fruits
         .select()
         .join(subquery, on=(
             (Fruits.price == subquery.c.min) &
             (Fruits.type == subquery.c.type)
        )))

这行得通，但我不明白它在做什么。 subquery.c 是怎么回事，为什么子查询有别名？