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\ d评论PostgreSQL的SQL语句:无法获取所需的最新/最近的评论,需要显示了最新评论
Table "public.comments"
Column | Type | Modifiers
------------+------------------------+-------------------------------------------------------
id | integer | not null default nextval('comments_id_seq'::regclass)
post_id | integer | not null
name | character varying(255) | not null
email | character varying(255) | not null
content | character varying(500) | not null
created_at | date |
updated_at | date |
Indexes:
"comments_pkey" PRIMARY KEY, btree (id)
对于这一说法
select post_id,created_at from comments order by created_at limit 5;
独特posts.title我
post_id | created_at
---------+------------
5 | 2011-07-11
5 | 2011-07-11
5 | 2011-07-11
8 | 2011-07-11
2 | 2011-07-17
(5 rows)
但我需要这样
结果0post_id | created_at
---------+------------
5 | 2011-07-11
8 | 2011-07-11
2 | 2011-07-17
(3 rows)
我该如何重写sql语句来获得这三行作为结果?
\ d柱
Table "public.posts"
Column | Type | Modifiers
-------------+------------------------+----------------------------------------------------
id | integer | not null default nextval('posts_id_seq'::regclass)
title | character varying(100) | not null
content | character varying(500) | not null
created_at | date |
updated_at | date |
tags | character varying(55) | not null default '50'::character varying
category_id | integer | not null default 1
Indexes:
"posts_pkey" PRIMARY KEY, btree (id)
与来自三行我需要从职位表中的posts.title三个ID。 我如何编写sql语句来获取post.titt与comments.post_id = 5或8或2?
我需要得到那些不同的posts.title最新评论。 – shibly
@guru:我已经更新了答案。 –
你为什么使用MAX函数?我需要最新comments.id的结果,这意味着通过created_at创建了comments.id命令。然后我需要内部加入posts.id来获得posts.title。 – shibly