Postgres通过查询分组 [英] Postgres group by query

问题描述

我试图在postgres的查询中使用group by。我无法按照我的需要将它工作，以便根据需要对结果进行分组。

I am trying to use group by in a query in postgres. I cannot get it to work as I would like in order to group results as I need.

这是对 recursion queries我刚刚回答了。但是现在我需要能够将结果分组到最终查询的root_id列。这是以前的查询：

This is an extension to another stack question on recursion queries I just had answered. But now I need to be able to group the results on the root_id column of the final query. Here is the query before:

select cl.parent_comment_id, 
     cl.article_comment_id,
     cl.comment, 
     cl.article_id,
     cl.comment_depth
from comment_list cl
order by cl.root_id, cl.article_comment_id, cl.comment_depth;

以下是我想要做的事情，以便将具有相同parent_comment_id的任何记录保存在一起。 / p>

Here is what I would like to do so that any records with the same parent_comment_id are kept together.

select cl.parent_comment_id, 
     cl.article_comment_id,
     cl.comment, 
     cl.article_id,
     cl.comment_depth
from comment_list cl
group by cl.parent_comment_id
order by cl.parent_comment_id, cl.article_comment_id, cl.comment_depth;

可以有多个记录返回相同的parent_comment_id，但是对于任何给定的article_comment_id都有不同的记录。即每个评论都是唯一的（标识，评论，标题等），但每个父评论可以有许多孩子。这已经被递归查询检索出来了，现在我只是试图将它们正确分组。

There can be many records with the same parent_comment_id returned, but distinct records for any given article_comment_id. i.e. each comment is unique (id, comment, title, etc.) but each parent comment can have many children. This has already been retrieved by the recursive query, now I am just trying to group them correctly.

编辑：

查看 http：/ /www.sqlfiddle.com/#!12/77771/2 。我希望article_comment_id = 6紧跟在article_comment_id = 3之后，因为id = 3是父级。然后article_comment_id = 4。

Take a look at http://www.sqlfiddle.com/#!12/77771/2 .What I would like is for article_comment_id=6 to follow immediately below article_comment_id=3 since id=3 is the parent. Then article_comment_id=4.

但我认为这需要程序化地完成。

However I am thinking this needs to be done procedurally.

所以我认为这是一个'没关系'的问题类型的问题，除非有人知道如何（这就是为什么我要放弃它）。但我认为我会尝试以程序方式解决这个问题。

So I think this is a 'never mind' type of question unless someone knows how (which is why I am leaving it up). But I think I am going to try to solve this part procedurally.

推荐答案

对于递归查询，您可以创建分层路径使用0填充字符串的技巧： SQL小提琴

For your recursive query, you can create a hierarchical path using this trick with 0-padded strings: SQL Fiddle

with recursive comment_list(article_comment_id, parent_comment_id, comment, article_id, comment_depth, comment_path) AS (
    select c.article_comment_id, 
           c.parent_comment_id, 
           c.comment, 
           c.article_id, 
           c.comment_depth,
           substr(CAST(1000000000+c.article_comment_id as varchar(1000)),2)
    from test_comment c
    where article_id = 100
      and parent_comment_id = 0

  union all

    select c.article_comment_id, 
           c.parent_comment_id, 
           c.comment, 
           c.article_id, 
           c.comment_depth,
           cl.comment_path || substr(CAST(1000000000+c.article_comment_id as varchar(1000)),2)
    from test_comment c
       join comment_list cl on c.parent_comment_id = cl.article_comment_id
)
select cl.article_comment_id,
     cl.comment_path, 
     cl.parent_comment_id,
     cl.comment, 
     cl.article_id,
     cl.comment_depth
from comment_list cl
order by cl.comment_path, cl.article_comment_id, cl.comment_depth;

---

删除GROUP BY。你想分组他们的显示，这是真正的ORDER BY

---

Drop the GROUP BY. You want to "group" them for display, which is really "ORDER BY"

select cl.parent_comment_id, 
     cl.article_comment_id,
     cl.comment, 
     cl.article_id,
     cl.comment_depth
from comment_list cl
order by cl.parent_comment_id, cl.article_comment_id, cl.comment_depth;

您可能需要也可能不需要 cl.root_id 按顺序排列，因此它可以是

You may or may not still need the cl.root_id in the order by, so it could be

order by cl.root_id, cl.parent_comment_id, cl.article_comment_id, cl.comment_depth;

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