[英]Ordering a WITH RECURSIVE query in Postgres
我在Postgres中执行递归查询以检索电子邮件及其线程子项列表,如下所示:
WITH RECURSIVE cte (id, title, path, parent_id, depth) AS (
SELECT id,
title,
array[id] AS path,
parent_id,
1 AS depth
FROM emails
WHERE parent_id IS NULL
UNION ALL
SELECT emails.id,
emails.title,
cte.path || emails.id,
emails.parent_id,
cte.depth + 1 AS depth
FROM emails
JOIN cte ON emails.parent_id = cte.id
)
SELECT id, title, path, parent_id, depth FROM cte
ORDER BY path;
如何在查找儿童电子邮件之前更改列表的顺序(例如,对标题进行排序)。 我显然需要保留外部ORDER BY,以便按照树的顺序检索列表,Postgres不允许我在UNION ALL之前插入ORDER BY子句。
谢谢,
创建一个由查询的第一部分组成的视图,按标题排序。 也许是这样的?
CREATE VIEW title_Sort AS
SELECT id,
title,
array[id] AS path,
parent_id,
1 AS depth
FROM emails
WHERE parent_id IS NULL
ORDER BY title;
然后UNION ALL使用您之前执行的其他查询查看。 我认为这会奏效。 在我的上网本上,所以我无法测试:/
这是未经测试的,但通常我可以在联合之前添加任何ORDER BY,只要有括号...
WITH RECURSIVE cte (id, title, path, parent_id, depth) AS (
( SELECT id,
title,
array[id] AS path,
parent_id,
1 AS depth
FROM emails
WHERE parent_id IS NULL
ORDER BY title
)
UNION ALL
SELECT emails.id,
emails.title,
cte.path || emails.id,
emails.parent_id,
cte.depth + 1 AS depth
FROM emails
JOIN cte ON emails.parent_id = cte.id
)
SELECT id, title, path, parent_id, depth FROM cte
ORDER BY path;
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