PostgreSQL，Groupwise最小值和最大值

Question

我有一张表;

CREATE TABLE public.user_locations 
(
    id integer NOT NULL DEFAULT nextval('user_locations_id_seq'::regclass), 
    user_id integer, 
    created_at timestamp without time zone, 
    location geography(Point,4326), 
    cluster_id integer, 
    CONSTRAINT user_locations_pkey PRIMARY KEY (id) 
) 
WITH (
    OIDS=FALSE 
); 

CREATE INDEX index_user_locations_on_location 
    ON public.user_locations 
    USING gist 
    (location); 

CREATE INDEX index_user_locations_on_user_id 
    ON public.user_locations 
    USING btree 
    (user_id); 

我想获得的最小和最大created_at值为每个集群为特定用户。这样我就会看到用户在群集中停留了多久。

目前我这样做;

SELECT * FROM (
    (
    SELECT DISTINCT ON (cluster_id) * FROM user_locations 
    WHERE user_id = 6 
    ORDER BY cluster_id, created_at DESC 
) 
    UNION 
    (
    SELECT DISTINCT ON (cluster_id) * FROM user_locations 
    WHERE user_id = 6 
    ORDER BY cluster_id, created_at ASC 
) 
) a 
ORDER BY cluster_id, created_at 

我认为这不是一个好的解决方案。这是对我的问题正确的查询？如果不是，您能否提出更好的方法来为特定用户检索每个群集的最小值和最大值？

Answer 1

这是窗函数是：

select id, user_id, cluster_id, location, 
     created_at, 
     min(created_at) over (partition by cluster_id) as min_created, 
     max(created_at) over (partition by cluster_id) as max_created 
    from user_locations 
    where user_id = 6 
    order by cluster_id, created_at