Question

我需要递归查询的帮助。假设下表：

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及其子女的列表：

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，还可以按名称对第一级项目进行排序？例如，所需的输出将是：

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不起作用：**

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;

以上将保留父子关系（孩子跟随他们的父母），但是应用任何其他ORDER BY子句（即：名称 - 就像某些人建议的那样）将导致结果失去它的父子关系。

Answer 1

另见关于PostgreSQL中CTE的这篇（已翻译）文章：wiki.phpfreakz.nl

编辑：尝试使用数组：

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;

PostgreSQL递归

1 个答案: