使用PostgreSQL获取聚合的、按SQL分组的查询的主键
我正在努力使用PostgreSQL创建一个包含聚合的SQL查询。考虑下面的表格:使用PostgreSQL获取聚合的、按SQL分组的查询的主键,sql,postgresql,Sql,Postgresql,我正在努力使用PostgreSQL创建一个包含聚合的SQL查询。考虑下面的表格: CREATE TABLE thing ( id INT NOT NULL PRIMARY KEY, price NUMERIC(10,2) NOT NULL, description VARCHAR(255) NOT NULL, url VARCHAR(255) NOT NULL, location_id INT NOT NULL REFERENCES location(id) ) CREAT
CREATE TABLE thing (
id INT NOT NULL PRIMARY KEY,
price NUMERIC(10,2) NOT NULL,
description VARCHAR(255) NOT NULL,
url VARCHAR(255) NOT NULL,
location_id INT NOT NULL REFERENCES location(id)
)
CREATE TABLE location (
id INT NOT NULL PRIMARY KEY,
type INT NOT NULL,
name VARCHAR(255) NOT NULL
)
现在,我想获得location.type=xxx且价格最低的每个地点的所有物品记录
比如:
SELECT min(price) FROM thing
INNER JOIN location ON (thing.location_id = location.id)
WHERE type = xxx
GROUP BY location_id
这将列出xxx类型的每个位置的最低价格,但如何从表thing中获取这些列的行(或其主键)?使用此
PostgreSQL
扩展名:
SELECT DISTINCT ON (location.id) thing.*
FROM location
JOIN thing
ON thing.location_id = location_id
WHERE type = 1
ORDER BY
location.id ASC, price ASC
这将仅为每个位置.id
选择第一行
由于您的行是按location.id
排序的,然后是按price
排序的,因此这将是具有最小价格的行
在新的PostgreSQL 8.4
中,您还可以使用窗口功能:
SELECT *
FROM (
SELECT thing.*, ROW_NUMBER() OVER (PARTITION BY location_id ORDER BY price) AS rn
FROM location
JOIN thing
ON thing.location_id = location_id
WHERE type = 1
) q
WHERE rn = 1
也许可以使用子查询
SELECT t.id,t.description,t.price FROM
( SELECT location_id, min(price) FROM thing
INNER JOIN location ON (thing.location_id = location.id)
WHERE type = xxx
GROUP BY location_id
) AS lowest
INNER JOIN thing AS t
ON t. location_id = lowest.location_id;
我是一名SQL Server人员,但以下内容应符合SQL-92标准,并应能正常工作:
select th.*
from thing th
inner join (select lo.id, min(th.price) minPrice
from location lo
inner join thing th
on th.location_id = lo.id
where lo.type = xxx
group by lo.id) minSet
on minSet.id = th.location_id
and th.price = minSet.minPrice
还要注意的是,我没有设置要测试的表,所以其中可能有一两个输入错误
虽然它确实有效,但看起来确实很尴尬。如果Postgres有类似SQL的排名函数,它们会使它更简单。试试这个查询
select thing.id,thing.description,thing.url,low.location_id,low.minimum from
(select thing.location_id,min(price) as minimum from thing
join location on thing.location_id=location.id
where location.type = 13 group by location_id) as low
inner join thing on thing.location_id = low.location_id
太好了,这正是我想要的。这也是我最初想到的。这个查询的问题是,如果最低价格不是唯一的,它将返回一个位置的多个thing列。根据描述,我认为这就是您要查找的。如果存在基于最低价格的重复内容,您希望选择哪一个?(反问句,因为您已经有了答案——row_number()是一个非常有用的扩展。)