postgresql – 使用Query遞迴查詢父

我正在使用postgresql.我的桌子如下所示

parent_idchild_id
----------------------
101102
103104
104105
105106

我想寫一個sql查詢,它將給出輸入的最終父級.

假設我以106作為輸入,則其輸出為103.

(106 --> 105 --> 104 --> 103)

這是一個完整的例子.首先是DDL：

test=> CREATE TABLE node (
test(>id SERIAL,
test(>label TEXT NOT NULL, -- name of the node
test(>parent_id INT,
test(>PRIMARY KEY(id)
test(> );
NOTICE:CREATE TABLE will create implicit sequence "node_id_seq" for serial column "node.id"
NOTICE:CREATE TABLE / PRIMARY KEY will create implicit index "node_pkey" for table "node"
CREATE TABLE

…和一些資料…

test=> INSERT INTO node (label, parent_id) VALUES ('n1',NULL),('n2',1),('n3',2),('n4',3);
INSERT 0 4
test=> INSERT INTO node (label) VALUES ('garbage1'),('garbage2'), ('garbage3');
INSERT 0 3
test=> INSERT INTO node (label,parent_id) VALUES ('garbage4',6);
INSERT 0 1
test=> SELECT * FROM node;
id |label| parent_id 
----+----------+-----------
 1 | n1|
 2 | n2|1
 3 | n3|2
 4 | n4|3
 5 | garbage1 |
 6 | garbage2 |
 7 | garbage3 |
 8 | garbage4 |6
(8 rows)

這對節點中的每個id執行遞迴查詢：

test=> WITH RECURSIVE nodes_cte(id, label, parent_id, depth, path) AS (
 SELECT tn.id, tn.label, tn.parent_id, 1::INT AS depth, tn.id::TEXT AS path 
 FROM node AS tn 
 WHERE tn.parent_id IS NULL
UIO/">NION ALL
 SELECT c.id, c.label, c.parent_id, p.depth + 1 AS depth, 
(p.path || '->' || c.id::TEXT) 
 FROM nodes_cte AS p, node AS c 
 WHERE c.parent_id = p.id
)
SELECT * FROM nodes_cte AS n ORDER BY n.id ASC;
id |label| parent_id | depth |path
----+----------+-----------+-------+------------
 1 | n1||1 | 1
 2 | n2|1 |2 | 1->2
 3 | n3|2 |3 | 1->2->3
 4 | n4|3 |4 | 1->2->3->4
 5 | garbage1 ||1 | 5
 6 | garbage2 ||1 | 6
 7 | garbage3 ||1 | 7
 8 | garbage4 |6 |2 | 6->8
(8 rows)

這得到所有後代WHERE node.id = 1：

test=> WITH RECURSIVE nodes_cte(id, label, parent_id, depth, path) AS (
 SELECT tn.id, tn.label, tn.parent_id, 1::INT AS depth, tn.id::TEXT AS path FROM node AS tn WHERE tn.id = 1
UNION ALL
 SELECT c.id, c.label, c.parent_id, p.depth + 1 AS depth, (p.path || '->' || c.id::TEXT) FROM nodes_cte AS p, node AS c WHERE c.parent_id = p.id
)
SELECT * FROM nodes_cte AS n;
id | label | parent_id | depth |path
----+-------+-----------+-------+------------
 1 | n1||1 | 1
 2 | n2|1 |2 | 1->2
 3 | n3|2 |3 | 1->2->3
 4 | n4|3 |4 | 1->2->3->4
(4 rows)

以下將獲取節點的ID為4的路徑：

test=> WITH RECURSIVE nodes_cte(id, label, parent_id, depth, path) AS (
 SELECT tn.id, tn.label, tn.parent_id, 1::INT AS depth, tn.id::TEXT AS path 
 FROM node AS tn 
 WHERE tn.parent_id IS NULL
UNION ALL
 SELECT c.id, c.label, c.parent_id, p.depth + 1 AS depth, 
(p.path || '->' || c.id::TEXT) 
 FROM nodes_cte AS p, node AS c 
 WHERE c.parent_id = p.id
)
SELECT * FROM nodes_cte AS n WHERE n.id = 4;
id | label | parent_id | depth |path
----+-------+-----------+-------+------------
 4 | n4|3 |4 | 1->2->3->4
(1 row)

讓我們假設你想限制搜尋到深度小於3的後代(請注意,深度還沒有增加)：

test=> WITH RECURSIVE nodes_cte(id, label, parent_id, depth, path) AS (
SELECT tn.id, tn.label, tn.parent_id, 1::INT AS depth, tn.id::TEXT AS path 
FROM node AS tn WHERE tn.id = 1
UNION ALL
SELECT c.id, c.label, c.parent_id, p.depth + 1 AS depth, 
(p.path || '->' || c.id::TEXT) 
FROM nodes_cte AS p, node AS c 
WHERE c.parent_id = p.id AND p.depth < 2
)
SELECT * FROM nodes_cte AS n;
 id | label | parent_id | depth | path 
----+-------+-----------+-------+------
1 | n1||1 | 1
2 | n2|1 |2 | 1->2
(2 rows)

我建議使用ARRAY資料型別而不是用於演示“路徑”的字串,但箭頭更多地說明了父<=>子關係.