使用树顺序从表中选择行

Question

我有表女巫包含字段:id,parent_id,name(等)

我想在"树旅行顺序"中订购此表,即.

id  parent_id
1,  0
3,  1
5,  1

2,  0
8,  2

4,  0
9,  4

(......)

总之描述:取根节点,追加所有子节点,取下一个根节点追加子节点等.

Answer 1

根据你的描述,我假设你的意思是广度优先,可以使用WITH RECURSIVE查询(PostgreSQL 8.4+)轻松完成:

WITH RECURSIVE tree 
AS 
(
    SELECT 
        node_name, id, parent_id, NULL::varchar AS parent_name 
    FROM foo 
    WHERE parent_id IS NULL 
    UNION
    SELECT 
        node_name, f1.id, f1.parent_id, tree.node_name AS parent_name 
    FROM 
        tree 
        JOIN foo f1 ON f1.parent_id = tree.id
) 
SELECT node_name, empno, parent_id, node_name FROM tree;

您还可以使用以下SQL来使用深度优先顺序:

WITH RECURSIVE tree 
AS 
(
    SELECT 
        node_name, id, parent_id, NULL::varchar AS parent_name, id::text AS path 
    FROM foo WHERE parent_id IS NULL 
    UNION
    SELECT 
        node_name, f1.id, f1.parent_id, tree.node_name AS parent_name, tree.path || '-' || f1.id::text AS path 
    FROM 
        tree 
        JOIN foo f1 ON f1.parent_id = tree.id
) 
SELECT node_name, empno, parent_id, node_name, path FROM tree ORDER BY path;

Answer 2

由于注意到了协同，通过提供深度优先顺序的解决方案迪奥戈Biazus会为ID不工作与不同的位数。

但是您可以改用此解决方案，它使用integer数组：

WITH RECURSIVE tree 
AS 
(
    SELECT 
        node_name, id, parent_id, NULL::varchar AS parent_name, array[id] AS path 
    FROM foo WHERE parent_id IS NULL 
    UNION
    SELECT 
        node_name, f1.id, f1.parent_id, tree.node_name AS parent_name, tree.path || f1.id AS path 
    FROM 
        tree 
        JOIN foo f1 ON f1.parent_id = tree.id
) 
SELECT node_name, empno, parent_id, node_name, path FROM tree ORDER BY path;