具有RECURSIVE CTE的Postgres：按照受欢迎程度对儿童进行排序/排序，同时保留树形结构（父母总是高于儿童）

时间：2017-02-14 19:04:02

标签： sql postgresql recursion parent-child common-table-expression

我正在建立一个论坛，非常像Reddit / Slashdot，即

  • 无限回复嵌套级别
  • 热门评论（按喜欢/投票排序）将升至顶部（在他们自己的嵌套/深度级别内），但树结构需要保留（父级总是直接显示在儿童上方）

这是一个示例表＆amp;数据：

DROP TABLE IF EXISTS "comments";
CREATE TABLE comments (
  id BIGINT PRIMARY KEY,
  parent_id BIGINT,
  body TEXT NOT NULL,
  like_score BIGINT,
  depth BIGINT
);

INSERT INTO comments VALUES (  0, NULL, 'Main top of thread post', 5 , 0 );

INSERT INTO comments VALUES (  1, 0, 'comment A', 5 , 1 );
INSERT INTO comments VALUES (  2, 1,    'comment A.A', 3, 2 );
INSERT INTO comments VALUES (  3, 1,    'comment A.B', 1, 2 );
INSERT INTO comments VALUES (  9, 3,    'comment A.B.A', 10, 3 );
INSERT INTO comments VALUES ( 10, 3,    'comment A.B.B', 5, 3 );
INSERT INTO comments VALUES ( 11, 3,    'comment A.B.C', 8, 3 );
INSERT INTO comments VALUES (  4, 1,    'comment A.C', 5, 2 );

INSERT INTO comments VALUES ( 5, 0, 'comment B', 10, 1 );
INSERT INTO comments VALUES ( 6, 5, 'comment B.A', 7, 2 );
INSERT INTO comments VALUES ( 7, 5, 'comment B.B', 5, 2 );
INSERT INTO comments VALUES ( 8, 5, 'comment B.C', 2, 2 );

这是我到目前为止提出的递归查询，但我无法弄清楚如何订购子项，但保留树结构（父项应始终高于子项）。 

WITH RECURSIVE tree AS (
  SELECT
    ARRAY[]::BIGINT[] AS sortable,
    id,
    body,
    like_score,
    depth
  FROM "comments"
  WHERE parent_id IS NULL

  UNION ALL

  SELECT
    tree.sortable ||  "comments".like_score || "comments".id,
    "comments".id,
    "comments".body,
    "comments".like_score,
    "comments".depth
  FROM "comments", tree
  WHERE "comments".parent_id = tree.id
)
SELECT * FROM tree
ORDER BY sortable DESC

这输出...... 

+----------------------------------------------------------+
|sortable      |id|body                   |like_score|depth|
+----------------------------------------------------------+
|{10,5,7,6}    |6 |comment B.A            |7         |2    |
|{10,5,5,7}    |7 |comment B.B            |5         |2    |
|{10,5,2,8}    |8 |comment B.C            |2         |2    |
|{10,5}        |5 |comment B              |10        |1    |
|{5,1,5,4}     |4 |comment A.C            |5         |2    |
|{5,1,3,2}     |2 |comment A.A            |3         |2    |
|{5,1,1,3,10,9}|9 |comment A.B.A          |10        |3    |
|{5,1,1,3,8,11}|11|comment A.B.C          |8         |3    |
|{5,1,1,3,5,10}|10|comment A.B.B          |5         |3    |
|{5,1,1,3}     |3 |comment A.B            |1         |2    |
|{5,1}         |1 |comment A              |5         |1    |
|              |0 |Main top of thread post|5         |0    |
+----------------------------------------------------------+

...但请注意＆＃34;评论B＆＃34;，＆＃34;评论A＆＃34;和＆＃34;主要帖子＆＃34;在他们的孩子下面？如何保留上下文顺序？即我想要的输出是：

+----------------------------------------------------------+
|sortable      |id|body                   |like_score|depth|
+----------------------------------------------------------+
|              |0 |Main top of thread post|5         |0    |
|{10,5}        |5 |comment B              |10        |1    |
|{10,5,7,6}    |6 |comment B.A            |7         |2    |
|{10,5,5,7}    |7 |comment B.B            |5         |2    |
|{10,5,2,8}    |8 |comment B.C            |2         |2    |
|{5,1}         |1 |comment A              |5         |1    |
|{5,1,5,4}     |4 |comment A.C            |5         |2    |
|{5,1,3,2}     |2 |comment A.A            |3         |2    |
|{5,1,1,3}     |3 |comment A.B            |1         |2    |
|{5,1,1,3,10,9}|9 |comment A.B.A          |10        |3    |
|{5,1,1,3,8,11}|11|comment A.B.C          |8         |3    |
|{5,1,1,3,5,10}|10|comment A.B.B          |5         |3    |
+----------------------------------------------------------+

我实际上希望用户能够通过多种方法进行排序：

  • 最受欢迎的第一个
  • 最不受欢迎的第一个
  • 最新的
  • 最早的
  • 等

......但在所有情况下，父母都需要在孩子的上方展示。但我只是在使用＆＃34; like_score＆＃34;在这里作为例子，我应该能够从那里找出其余部分。

花了很多时间研究网络并亲自尝试，感觉我已经接近了，但无法弄清楚这最后一部分。

2 个答案:

答案 0 :(得分：2)

1 

tree.sortable ||  -"comments".like_score || "comments".id
                  ^
                 /|\
                  |
                  |

2 

ORDER BY sortable  

WITH RECURSIVE tree AS (
  SELECT
    ARRAY[]::BIGINT[] AS sortable,
    id,
    body,
    like_score,
    depth
  FROM "comments"
  WHERE parent_id IS NULL

  UNION ALL

  SELECT
    tree.sortable ||  -"comments".like_score || "comments".id,
    "comments".id,
    "comments".body,
    "comments".like_score,
    "comments".depth
  FROM "comments", tree
  WHERE "comments".parent_id = tree.id
)
SELECT * FROM tree
ORDER BY sortable 

+-------------------+----+-------------------------+------------+-------+
| sortable          | id | body                    | like_score | depth |
+-------------------+----+-------------------------+------------+-------+
| (null)            | 0  | Main top of thread post | 5          | 0     |
+-------------------+----+-------------------------+------------+-------+
| {-10,5}           | 5  | comment B               | 10         | 1     |
+-------------------+----+-------------------------+------------+-------+
| {-10,5,-7,6}      | 6  | comment B.A             | 7          | 2     |
+-------------------+----+-------------------------+------------+-------+
| {-10,5,-5,7}      | 7  | comment B.B             | 5          | 2     |
+-------------------+----+-------------------------+------------+-------+
| {-10,5,-2,8}      | 8  | comment B.C             | 2          | 2     |
+-------------------+----+-------------------------+------------+-------+
| {-5,1}            | 1  | comment A               | 5          | 1     |
+-------------------+----+-------------------------+------------+-------+
| {-5,1,-5,4}       | 4  | comment A.C             | 5          | 2     |
+-------------------+----+-------------------------+------------+-------+
| {-5,1,-3,2}       | 2  | comment A.A             | 3          | 2     |
+-------------------+----+-------------------------+------------+-------+
| {-5,1,-1,3}       | 3  | comment A.B             | 1          | 2     |
+-------------------+----+-------------------------+------------+-------+
| {-5,1,-1,3,-10,9} | 9  | comment A.B.A           | 10         | 3     |
+-------------------+----+-------------------------+------------+-------+
| {-5,1,-1,3,-8,11} | 11 | comment A.B.C           | 8          | 3     |
+-------------------+----+-------------------------+------------+-------+
| {-5,1,-1,3,-5,10} | 10 | comment A.B.B           | 5          | 3     |
+-------------------+----+-------------------------+------------+-------+

答案 1 :(得分：0)

检查一下：

WITH RECURSIVE tree AS (
  SELECT
    ARRAY[]::BIGINT[] AS sortable,
    id,
    body,
    like_score,
    depth,
    lpad(id::text, 2, '0') as path
  FROM "comments"
  WHERE parent_id IS NULL

  UNION ALL

  SELECT
    tree.sortable ||  "comments".like_score || "comments".id,
    "comments".id,
    "comments".body,
    "comments".like_score,
    "comments".depth,
    tree.path || '/' || lpad("comments".id::text, 2, '0') as path
  FROM "comments", tree
  WHERE "comments".parent_id = tree.id
)
SELECT * FROM tree
ORDER BY path

请注意，您可以将2上的参数lpad替换为您想要的任意位数。

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