我正在尝试编写一个使用 Nested Interval Hierarchy 的 SQL 查询数据库模型。
--Given a parent Id, this query retrieves the position of the youngest child which can be inserted into the table
SELECT TOP 1
--compute values based on the youngest "sibling id" (the one with the highest value)
(parent.m_11 * (FLOOR(child.m_11/child.m_12)+2) - parent.m_12) as m_11,
(parent.m_11) as m_12,
(parent.m_21 * (FLOOR(child.m_11/child.m_12)+2) - parent.m_22) as m_21,
(parent.m_21) as m_22
FROM my_so_table child
--grabs all children of the parent
JOIN my_so_table parent
ON parent.Id = 1
AND parent.m_21 = child.m_22
AND parent.m_11 = child.m_12
--the operation "Floor(child.m_11 / child.m_12) is the siblingId that I need to do math on above
ORDER By FLOOR(child.m_11/child.m_12) DESC
GO
有模式:
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[my_so_table](
[m_11] [int] NOT NULL,
[m_12] [int] NOT NULL,
[m_21] [int] NOT NULL,
[m_22] [int] NOT NULL,
[Id] [int] IDENTITY(1,1) NOT NULL)
GO
INSERT INTO [dbo].[my_so_table] VALUES (2,1,1,0); --1.
INSERT INTO [dbo].[my_so_table] VALUES (3,1,1,0); --2.
INSERT INTO [dbo].[my_so_table] VALUES (3,2,2,1); --1.1
INSERT INTO [dbo].[my_so_table] VALUES (4,1,1,0); --3.
使用上述架构,使用 1
的 parentId 运行上述查询正确返回
5,2,3,1
它正确地表示要插入到 Id 为 1 的父节点下的新节点的矩阵。在 2
的 parentId 上运行上述查询返回一个空列表,当它应该返回时
5,3,2,1
表示 id 为 2 的父项下的第一个子项的矩阵。
这是错误的,因为我的查询没有处理没有父项的子项的情况。如果没有 parent 的 child ,Floor(child.m_11 / child.m_12)
的结果应该是-1。我如何更改我的查询以完成此操作?
最佳答案
我找到了我的解决方案。我一直在回避 greatest-n-by-group
,而实际上我不明白 group-by
是如何工作的。
--Given a parent Id, this query retrieves the position of the youngest child which can be inserted into the table
--insert into my_so_table(m_11, m_12, m_21, m_22)
SELECT TOP 1
--compute values based on the youngest 'sibling id' (the one with the highest value)
(parent.m_11 * (ISNULL(siblingId, 0) + 2) - parent.m_12) as m_11,
(parent.m_11) as m_12,
(parent.m_21 * (ISNULL(siblingId, 0) + 2) - parent.m_22) as m_21,
(parent.m_21) as m_22
FROM my_so_table parent
--grabs all children of the parent
LEFT JOIN (
--Grabs the youngest sibling for each sibling chain
SELECT
child.m_12,
child.m_22,
Max(Floor(child.m_11 / child.m_12)) as siblingId
FROM my_so_table child
Group By child.m_12, child.m_22
) child
on(parent.m_21 = child.m_22)
AND(parent.m_11 = child.m_12)
WHERE parent.Id = @parentId
ORDER By siblingId DESC
GO
group-by
之前没有工作,因为我无法从子查询中检索到 m_12
和 m_22
,因为我不是t group by
这两个值。切换到左连接会导致报告空值,这正是我所需要的!
关于选择查询中的 SQL 条件变量,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/42141154/