sql - Postgresql 复制树表内的数据

Question

我有一个树形结构的表，列是id、category、parent_id

现在我需要将一个节点及其子节点复制到另一个节点，在复制时，类别必须相同，但具有新的 id 和 parent_id..

我的输入将是要复制的节点 & 要复制的目标节点

我已经在图像文件中解释了树结构..

我需要一个函数来这样做..,

PostgreSQL 版本 9.1.2

  Column   |  Type   |                    Modifiers                    
-----------+---------+-------------------------------------------------
 id        | integer | not null default nextval('t1_id_seq'::regclass)
 category  | text    | 
 parent_id | integer | 
Indexes:
    "t1_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
    "fk_t1_1" FOREIGN KEY (parent_id) REFERENCES t1(id)
Referenced by:
    TABLE "t1" CONSTRAINT "fk_t1_1" FOREIGN KEY (parent_id) REFERENCES t1(id)

Answer 1

(在 PostgreSQL 8.4.3 下测试)

以下查询为节点 4 下的子树分配新 ID(参见 nextval)，然后找到相应的新 ID of parents(参见 >左连接).

WITH RECURSIVE CTE AS (
    SELECT *, nextval('t1_id_seq') new_id FROM t1 WHERE id = 4
    UNION ALL
    SELECT t1.*, nextval('t1_id_seq') new_id FROM CTE JOIN t1 ON CTE.id = t1.parent_id
)
SELECT C1.new_id, C1.category, C2.new_id new_parent_id
FROM CTE C1 LEFT JOIN CTE C2 ON C1.parent_id = C2.id

结果(在您的测试数据上):

new_id  category    new_parent_id
------  --------    -------------
9       C4          
10      C5          9
11      C6          9
12      C7          10

一旦你有了它，就很容易将它插入回表中，你只需要小心地将子树根与适当的父节点重新连接(在这种情况下为 8，请参见 COALESCE(new_parent_id, 8)):

INSERT INTO t1
SELECT new_id, category, COALESCE(new_parent_id, 8) FROM (
    WITH RECURSIVE CTE AS (
        SELECT *, nextval('t1_id_seq') new_id FROM t1 WHERE id = 4
        UNION ALL
        SELECT t1.*, nextval('t1_id_seq') new_id FROM CTE JOIN t1 ON CTE.id = t1.parent_id
    )
    SELECT C1.new_id, C1.category, C2.new_id new_parent_id
    FROM CTE C1 LEFT JOIN CTE C2 ON C1.parent_id = C2.id
) Q1

之后，该表包含以下数据:

new_id  category    new_parent_id
------  --------    -------------
1       C1
2       C2          1
3       C3          1
4       C4          2
5       C5          4
6       C6          4
7       C7          5
8       C8          3
9       C4          8
10      C5          9
11      C6          9
12      C7          10