获取 leading/trailing 个条目的优化

Question

我正在尝试将 table 中的前导或尾随 x 条目获取到特定 ID。我目前的尝试确实工作得很好，但它看起来很笨拙，我想知道是否有办法改进它。

WITH tempTable AS ( SELECT *,ROW_NUMBER() OVER (ORDER BY created DESC) AS RN from byali.posts)
SELECT * from tempTable as nb1 WHERE RN IN (SELECT nb2.RN+i
             FROM tempTable AS nb2
             CROSS JOIN (SELECT a.n as i FROM generate_series(-10,-1) as a(n)) n
             WHERE nb2.id='188d9b6b-e398-407d-9cf4-e75ff121c32a')

这将 select ID 为

的条目之前的 10 个帖子

188d9b6b-e398-407d-9cf4-e75ff121c32a

Table结构：

CREATE TABLE byali.posts
(
    id uuid NOT NULL DEFAULT gen_random_uuid(),
    title text COLLATE pg_catalog."default",
    message text COLLATE pg_catalog."default",
    created timestamp with time zone DEFAULT now(),
    CONSTRAINT posts_pkey PRIMARY KEY (id)
)

和示例数据：

insert into byali.posts (title,message,created) VALUES ('title1','message1','2018-02-11 17:00:56.349611+01'),('title2','message2','2018-02-13 12:22:54.432413+01'),('title3','message3','2018-02-13 14:38:51.997999+01')

Answer 1

如果创建的列是唯一的，您可以使用以下查询在 ID = 188d9b6b-e398-407d-9cf4-e75ff121c32a 的条目之前获得 10 个帖子：

select *
from byali.posts
where created < (select created
                 from byali.posts
                 where id = '188d9b6b-e398-407d-9cf4-e75ff121c32a')
order by created desc
limit 10;

ID = 188d9b6b-e398-407d-9cf4-e75ff121c32a 的条目后有 10 个帖子

select *
from byali.posts
where created > (select created
                 from byali.posts
                 where id = '188d9b6b-e398-407d-9cf4-e75ff121c32a')
order by created
limit 10;

获取 leading/trailing 个条目的优化

Optimization of getting leading/trailing entries

postgresql

relational-database