我在SQL Server中有一个层次结构,有多个父级,但似乎无法获得我需要的结果集。
这就是我到目前为止所拥有的。
DECLARE @Table TABLE (ChildId varchar(max), ParentId varchar(max))
INSERT INTO @Table (ChildId,ParentId)
VALUES
('England',NULL),
('Cities',NULL),
('Towns',NULL),
('South West','England'),
('Bristol','South West'),
('Bristol','Cities'),
('Suburb','Bristol'),
('Thornbury','South West'),
('Thornbury','Towns');
WITH CTE (ChildId, ParentId, Level)
AS (
SELECT
ChildId,
ParentID,
0
FROM @Table
WHERE ParentID IS NULL
UNION ALL
SELECT
r.ChildId,
r.ParentId,
ct.Level + 1
FROM @Table r
JOIN CTE ct
ON ct.ChildId = r.ParentId
)
SELECT * FROM CTE order by childId, level
这给了我这个结果集:
ChildId | ParentId | Level
Bristol | Cities | 1
Bristol | South West | 2
Suburb | Bristol | 2
Suburb | Bristol | 3
Cities | NULL | 0
England | NULL | 0
South West | England | 1
Thornbury | Towns | 1
Thornbury | South West | 2
Towns | NULL | 0
但我也想要祖父母、曾祖父母和曾曾祖父母(等):
ChildId | ParentId | Level
Bristol | Cities | 1
Bristol | South West | 2
Bristol | England | <------------------------
Suburb | South West | <------------------------
Suburb | England | <------------------------
Suburb | Cities | <------------------------
等。
你试图做的事情至少在某种程度上类似于Ranganathan的分类。在这种情况下,您必须在层次结构中向上,而不是向下:
with cte as (
select t.ChildId, t.ParentId, 0 as [Lvl]
from @Table t
where t.ParentId is not null
union all
select c.ChildId, t.ParentId, c.Lvl + 1
from @Table t
inner join cte c on c.ParentId = t.ChildId
where t.ParentId is not null
)
select * from cte c order by c.ChildId, c.Lvl, c.ParentId;
编辑:更新了CTE递归部分中的WHERE
子句。看起来这是最初尝试的一些遗留物,我忘了考虑。.
使用递归表值函数而不是 CTE 怎么样:
CREATE FUNCTION tvf_GetParents
(
@childID VARCHAR(MAX),
@level INT
)
RETURNS
@output TABLE
(
ancestor VARCHAR(MAX),
level INT
)
AS
BEGIN
DECLARE @parentIDs TABLE (pID VARCHAR(MAX))
-- Get parent of child and add it to output
IF EXISTS (SELECT 1 FROM HTable WHERE ChildId = @childID AND ParentId IS NOT NULL)
BEGIN
INSERT @parentIDs
SELECT ParentId FROM HTable WHERE ChildId = @childID
INSERT INTO @output (ancestor, level)
SELECT pID, @level FROM @parentIDs
END
ELSE
RETURN
DECLARE @pID VARCHAR(MAX) = 0
-- Iterate over all parents (cursorless loop)
WHILE (1 = 1)
BEGIN
-- Get next ParentId
SELECT TOP 1 @pID = pID
FROM @parentIDs
WHERE pID > @pID
ORDER BY pID
-- Exit loop if no more parents
IF @@ROWCOUNT = 0 BREAK;
-- call function recursively so as to add to output
-- the rest of the ancestors (if any)
INSERT INTO @output (ancestor, level)
SELECT ancestor, level FROM tvf_GetParents(@pID, @level + 1)
END
RETURN
END
GO
使用上面的函数,您可以轻松获得所有子祖先对:
SELECT DISTINCT ChildId, ancestor, level
FROM HTable h
OUTER APPLY tvf_GetParents(h.ChildId, 0) AS p
ORDER BY ChildId, Level
输出:
ChildId ancestor level
------------------------------
Bristol Cities 0
Bristol South West 0
Bristol England 1
Cities NULL NULL
England NULL NULL
South West England 0
Suburb Bristol 0
Suburb Cities 1
Suburb South West 1
Suburb England 2
Thornbury South West 0
Thornbury Towns 0
Thornbury England 1
Towns NULL NULL
请注意,"级别"在这里有不同的含义:级别 NULL 表示无父级,级别 0 表示子级-父级记录,级别 1 表示子级-祖父母记录等。
另请注意,就 sql 服务器中递归函数的嵌套级别而言,存在限制。我认为是32。如果您的树深度超出该范围,那么我提出的解决方案将不起作用。
这是你要找的吗?
WITH CTE (ChildId, FirstChild, ParentId, Level)
AS (
SELECT
ChildId,
ChildId as FirstChild,
ParentID,
0
FROM @Table
WHERE ParentID IS NULL
UNION ALL
SELECT
r.ChildId,
ct.FirstChild,
r.ParentId,
ct.Level + 1
FROM @Table r
JOIN CTE ct
ON ct.ChildId = r.ParentId
)
SELECT ChildId,
ParentId,
Level
FROM CTE
UNION
SELECT FirstChild,
ParentId,
Level
FROM CTE
ORDER BY ChildId,
Level,
ParentId
输出:
ChildId ParentId Level
------- -------- -----
Bristol Cities 1
Bristol South West 2
Cities NULL 0
Cities Cities 1
Cities Bristol 2
England NULL 0
England England 1
England South West 2
England Bristol 3
South West England 1
Suburb Bristol 2
Suburb Bristol 3
Thornbury Towns 1
Thornbury South West 2
Towns NULL 0
Towns Towns 1