PostgreSQL递归 [英] PostgreSQL recursive with

问题描述

我需要有关递归查询的帮助。假定如下表：

I need help with a recursive query. Assuming the following table:

CREATE TEMPORARY TABLE tree (
    id        integer PRIMARY KEY,
    parent_id integer NOT NULL,
    name      varchar(50)
);    

INSERT INTO tree (id, parent_id, name) VALUES (3, 0, 'Peter'), (2,0, 'Thomas'), (5,2, 'David'), (1, 0, 'Rob'), (8, 0, 'Brian');

我可以使用以下查询检索所有人员及其子女的列表：

I can retrieve a list of all people and their children with the following query:

WITH RECURSIVE recursetree(id, parent_id) AS (
    SELECT id, parent_id FROM tree WHERE parent_id = 0
  UNION
    SELECT t.id, t.parent_id
    FROM tree t
    JOIN recursetree rt ON rt.id = t.parent_id
  )
SELECT * FROM recursetree;

如何按顺序列出它们，并按名称对第一级项目进行排序？例如，所需的输出将是：

How can I list them in order, and also sort the first level items by name? For example, the desired output would be:

id, parent_id, name    
8, 0, "Brian"
3, 0, "Peter"
1, 0; "Rob"
2, 0, "Thomas"
5, 2, "  David"

谢谢

**编辑。请注意，添加ORDER BY无效：**

**EDIT. Please note that adding an ORDER BY won't work: **

WITH RECURSIVE recursetree(id, parent_id, path, name) AS (
    SELECT 
        id, 
        parent_id, 
        array[id] AS path, 
        name 
    FROM tree WHERE parent_id = 0
  UNION ALL
    SELECT t.id, t.parent_id, rt.path || t.id, t.name
    FROM tree t
    JOIN recursetree rt ON rt.id = t.parent_id
  )
SELECT * FROM recursetree ORDER BY path;

以上内容将保留亲子关系（孩子跟随其父母），但应用任何其他ORDER BY子句（例如：name-如某些人所建议）将导致结果失去其父子关系。

The above will retain the parent child relationship (children follow their parents), but applying any other ORDER BY clause (ie: name - like some have suggested) will cause the result to lose it's parent-child relationships.

推荐答案

另请参见这篇有关PostgreSQL中CTE的文章（翻译的）： wiki.phpfreakz.nl

See also this (translated) article about CTE's in PostgreSQL: wiki.phpfreakz.nl

编辑：使用数组尝试以下操作：

Try this one, using an array:

WITH RECURSIVE recursetree(id, parent_ids, firstname) AS (
    SELECT id, NULL::int[] || parent_id, name FROM tree WHERE parent_id = 0
  UNION ALL
    SELECT 
    t.id, 
    rt.parent_ids || t.parent_id, 
    name
    FROM tree t
    JOIN recursetree rt ON rt.id = t.parent_id
  )
SELECT * FROM recursetree ORDER BY parent_ids;

这篇关于PostgreSQL递归的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！