[英]Postgres recursive query with row_to_json
我在 postgres 9.3.5 中有一張表,如下所示:
CREATE TABLE customer_area_node
(
id bigserial NOT NULL,
customer_id integer NOT NULL,
parent_id bigint,
name text,
description text,
CONSTRAINT customer_area_node_pkey PRIMARY KEY (id)
)
我查詢:
WITH RECURSIVE c AS (
SELECT *, 0 as level, name as path FROM customer_area_node WHERE customer_id = 2 and parent_id is null
UNION ALL
SELECT customer_area_node.*,
c.level + 1 as level,
c.path || '/' || customer_area_node.name as path
FROM customer_area_node
join c ON customer_area_node.parent_id = c.id
)
SELECT * FROM c ORDER BY path;
這似乎適用於構建諸如 building1/floor1/room1、building1/floor1/room2 等路徑。
我希望能夠輕松地將其轉換為表示樹結構的 json,我被告知我可以使用 row_to_json 來完成。
作為一種合理的替代方法,我可以通過任何其他方式將數據格式化為更有效的機制,這樣我實際上可以輕松地將其轉換為實際的樹結構,而無需在 / 上使用大量 string.splits。
有沒有一種相當簡單的方法可以用 row_to_json 做到這一點?
您不能使用通常的遞歸 CTE 來做到這一點,因為幾乎不可能在其層次結構的深處設置 json 值。 但是你可以反過來做:從葉子開始構建樹,直到它的根:
-- calculate node levels
WITH RECURSIVE c AS (
SELECT *, 0 as lvl
FROM customer_area_node
-- use parameters here, to select the root first
WHERE customer_id = 2 AND parent_id IS NULL
UNION ALL
SELECT customer_area_node.*, c.lvl + 1 as lvl
FROM customer_area_node
JOIN c ON customer_area_node.parent_id = c.id
),
-- select max level
maxlvl AS (
SELECT max(lvl) maxlvl FROM c
),
-- accumulate children
j AS (
SELECT c.*, json '[]' children -- at max level, there are only leaves
FROM c, maxlvl
WHERE lvl = maxlvl
UNION ALL
-- a little hack, because PostgreSQL doesn't like aggregated recursive terms
SELECT (c).*, array_to_json(array_agg(j)) children
FROM (
SELECT c, j
FROM j
JOIN c ON j.parent_id = c.id
) v
GROUP BY v.c
)
-- select only root
SELECT row_to_json(j) json_tree
FROM j
WHERE lvl = 0;
這甚至適用於 PostgreSQL 9.2+
更新:一個變體,它也應該處理流氓葉節點(位於 1 和max-level之間的級別):
WITH RECURSIVE c AS (
SELECT *, 0 as lvl
FROM customer_area_node
WHERE customer_id = 1 AND parent_id IS NULL
UNION ALL
SELECT customer_area_node.*, c.lvl + 1
FROM customer_area_node
JOIN c ON customer_area_node.parent_id = c.id
),
maxlvl AS (
SELECT max(lvl) maxlvl FROM c
),
j AS (
SELECT c.*, json '[]' children
FROM c, maxlvl
WHERE lvl = maxlvl
UNION ALL
SELECT (c).*, array_to_json(array_agg(j) || array(SELECT r
FROM (SELECT l.*, json '[]' children
FROM c l, maxlvl
WHERE l.parent_id = (c).id
AND l.lvl < maxlvl
AND NOT EXISTS (SELECT 1
FROM c lp
WHERE lp.parent_id = l.id)) r)) children
FROM (SELECT c, j
FROM c
JOIN j ON j.parent_id = c.id) v
GROUP BY v.c
)
SELECT row_to_json(j) json_tree
FROM j
WHERE lvl = 0;
這應該也適用於 PostgreSQL 9.2+,但是,我無法測試。 (我現在只能在 9.5+ 上測試)。
這些解決方案可以處理任何分層表中的任何列,但總是會在其輸出中附加一個int
類型的lvl
JSON 屬性。
很抱歉回答太晚了,但我想我找到了一個優雅的解決方案,可以成為這個問題的公認答案。
基於@pozs 發現的令人敬畏的“小技巧”,我想出了一個解決方案:
NOT EXISTS
謂詞)WITH RECURSIVE customer_area_tree("id", "customer_id", "parent_id", "name", "description", "children") AS (
-- tree leaves (no matching children)
SELECT c.*, json '[]'
FROM customer_area_node c
WHERE NOT EXISTS(SELECT * FROM customer_area_node AS hypothetic_child WHERE hypothetic_child.parent_id = c.id)
UNION ALL
-- pozs's awesome "little hack"
SELECT (parent).*, json_agg(child) AS "children"
FROM (
SELECT parent, child
FROM customer_area_tree AS child
JOIN customer_area_node parent ON parent.id = child.parent_id
) branch
GROUP BY branch.parent
)
SELECT json_agg(t)
FROM customer_area_tree t
LEFT JOIN customer_area_node AS hypothetic_parent ON(hypothetic_parent.id = t.parent_id)
WHERE hypothetic_parent.id IS NULL
更新:
使用非常簡單的數據進行測試,它確實有效,但正如 posz 在評論中指出的那樣,使用他的示例數據,一些流氓葉節點被遺忘了。 但是,我發現對於更復雜的數據,之前的答案也不起作用,因為只有具有“最大級別”葉節點的共同祖先的流氓葉節點才會被捕獲(當“1.2.5.8”不存在時,“ 1.2.4" 和 "1.2.5" 不存在,因為它們沒有具有任何“最大級別”葉節點的共同祖先)。
所以這是一個新的提議,通過提取NOT EXISTS
子請求並使其成為內部UNION
,利用UNION
重復數據刪除能力(利用 jsonb 比較能力)將 posz 的工作與我的工作混合:
<!-- language: sql -->
WITH RECURSIVE
c_with_level AS (
SELECT *, 0 as lvl
FROM customer_area_node
WHERE parent_id IS NULL
UNION ALL
SELECT child.*, parent.lvl + 1
FROM customer_area_node child
JOIN c_with_level parent ON parent.id = child.parent_id
),
maxlvl AS (
SELECT max(lvl) maxlvl FROM c_with_level
),
c_tree AS (
SELECT c_with_level.*, jsonb '[]' children
FROM c_with_level, maxlvl
WHERE lvl = maxlvl
UNION
(
SELECT (branch_parent).*, jsonb_agg(branch_child)
FROM (
SELECT branch_parent, branch_child
FROM c_with_level branch_parent
JOIN c_tree branch_child ON branch_child.parent_id = branch_parent.id
) branch
GROUP BY branch.branch_parent
UNION
SELECT c.*, jsonb '[]' children
FROM c_with_level c
WHERE NOT EXISTS (SELECT 1 FROM c_with_level hypothetical_child WHERE hypothetical_child.parent_id = c.id)
)
)
SELECT jsonb_pretty(row_to_json(c_tree)::jsonb)
FROM c_tree
WHERE lvl = 0;
進一步開發了 pozs 的答案,以獲得帶有子樹的遞歸葉子。 所以這個答案真的返回了完整的樹。
CREATE OR REPLACE FUNCTION pg_temp.getTree(bigint)
RETURNS TABLE(
id bigint,
customer_id integer,
parent_id bigint,
name text,
description text,
children json
)
AS $$
WITH RECURSIVE relations AS (
SELECT
can.id,
can.customer_id,
can.parent_id,
can.name,
can.description,
0 AS depth
FROM customer_area_node can
WHERE can.id = $1
UNION ALL
SELECT
can.id,
can.customer_id,
can.parent_id,
can.name,
can.description,
relations.depth + 1
FROM customer_area_node can
JOIN relations ON can.parent_id = relations.id AND can.id != can.parent_id
),
maxdepth AS (
SELECT max(depth) maxdepth FROM relations
),
rootTree as (
SELECT r.* FROM
relations r, maxdepth
WHERE depth = maxdepth
UNION ALL
SELECT r.* FROM
relations r, rootTree
WHERE r.id = rootTree.parent_id AND rootTree.id != rootTree.parent_id
),
mainTree AS (
SELECT
c.id,
c.customer_id,
c.parent_id,
c.name,
c.description,
c.depth,
json_build_array() children
FROM relations c, maxdepth
WHERE c.depth = maxdepth
UNION ALL
SELECT
(relations).*,
array_to_json(
array_agg(mainTree)
||
array(
SELECT t
FROM (
SELECT
l.*,
json_build_array() children
FROM relations l, maxdepth
WHERE l.parent_id = (relations).id
AND l.depth < maxdepth
AND l.id NOT IN (
SELECT id FROM rootTree
)
) r
JOIN pg_temp.getTree(r.id) t
ON r.id = t.id
))
children
FROM (
SELECT relations, mainTree
FROM relations
JOIN mainTree
ON (
mainTree.parent_id = relations.id
AND mainTree.parent_id != mainTree.id
)
) v
GROUP BY v.relations
)
SELECT
id,
customer_id,
parent_id,
name,
description,
children
FROM mainTree WHERE id = $1
$$
LANGUAGE SQL;
SELECT *
FROM
customer_area_node can
JOIN pg_temp.getTree(can.id) t ON t.id = can.id
WHERE can.parent_id IS NULL;
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