如何在 PostgreSQL 递归中有两个排序选项

Question

我有以下递归组织评论及其回复的查询。

WITH RECURSIVE comment_tree AS (
    SELECT 
        id                AS comment_id, 
        body              AS comment_body, 
        reply_to          AS comment_reply_to, 
        1                 AS level, 
        "createdAt"       AS comment_date, 
        commenter_id, 
        article_id, 
        array["createdAt"] AS path_info
   FROM "Comments" 
   WHERE "reply_to" IS NULL
   UNION ALL
   SELECT 
        c.id, 
        c.body, 
        c.reply_to, 
        p.level + 1, 
        "createdAt", 
        c.commenter_id, 
        c.article_id,
        p.path_info || c."createdAt"
   FROM "Comments" c
   JOIN comment_tree p ON c.reply_to = comment_id
)
SELECT 
    comment_id, 
    path_info,
    comment_body, 
    comment_reply_to, 
    comment_date, 
    level, 
    U.first_name, 
    U.last_name, 
    coalesce(U.username, CAST(U.id AS VARCHAR)) AS username
FROM comment_tree
LEFT JOIN 
    "Users" U ON commenter_id = U.id 
        WHERE article_id = '62834723-B804-4CA1-B984-D949B1A7E1E2'
ORDER BY path_info DESC;

据我所见...到目前为止，除了排序外，一切正常。

目前评论按从旧到新的顺序排列。然后正确地将回复嵌套在下面，但我希望父列表从最新到最旧。

有什么方法可以对子值 DESC 和父值 ASC 进行排序？

例如

+----+----------+----------+
| id | reply_to |   date   |
+----+----------+----------+
| C1 | null     | 01052016 | < - Oldest
| C2 | null     | 02052016 |
| C3 | C1       | 03052016 |
| C4 | C1       | 04052016 |
| C5 | null     | 05052016 |
| C6 | C4       | 06052016 |
| C7 | C2       | 07052016 |
| C8 | C6       | 08052016 | < - Newest 
|    |          |          |
+----+----------+----------+

想要的结果

| C5 (Newest Parent first)
| C2
  | C7
| C1
  | C3 (Oldest Child first for all tiers below parent)
  | C4
    | C6
      | C8

Answer 1

我会在 Common Table Expression.

中引入一个人工列 sort

Comments定义如下：

            Table "laurenz.Comments"
┌───────────┬───────────────────────┬───────────┐
│  Column   │         Type          │ Modifiers │
├───────────┼───────────────────────┼───────────┤
│ id        │ character varying(10) │ not null  │
│ reply_to  │ character varying(10) │           │
│ createdAt │ date                  │ not null  │
└───────────┴───────────────────────┴───────────┘
Indexes:
    "comment_tree_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
    "comment_tree_reply_to_fkey" FOREIGN KEY (reply_to) REFERENCES "Comments"(id)
Referenced by:
    TABLE ""Comments"" CONSTRAINT "comment_tree_reply_to_fkey" FOREIGN KEY (reply_to) REFERENCES "Comments"(id)

我会这样写：

WITH RECURSIVE comment_tree AS (
   SELECT id, reply_to, "createdAt",
          CAST(current_date - "createdAt" AS text) AS sort
      FROM "Comments"
      WHERE reply_to IS NULL
   UNION ALL SELECT c.id, c.reply_to, c."createdAt",
                    substring(p.sort FROM '^[^-]*') || '-' || c."createdAt"
      FROM "Comments" c
           JOIN comment_tree p ON c.reply_to = p.id
)
SELECT id, reply_to, "createdAt"
FROM comment_tree
ORDER BY sort;

如何在 PostgreSQL 递归中有两个排序选项

How to have two sort options in PostgreSQL RECURSIVE

postgresql

sql-order-by

recursive-query

common-table-expression