Question

我有这个概念代码（带一些注释）：

IF EXISTS (SELECT * FROM information_schema.schemata WHERE schema_name = 'test')
SET NOEXEC ON
GO

-- didn't use EXEC sp_executesql for Syntax Highlighting and Code Compeltion in MSSMS
CREATE SCHEMA [test]
GO

SET NOEXEC OFF
GO

BEGIN TRANSACTION

-- child is a list
CREATE TABLE [test].[Child] (
    [ChildId] BIGINT NOT NULL,
    CONSTRAINT [PK_Child] PRIMARY KEY CLUSTERED ([ChildId]) WITH (IGNORE_DUP_KEY = ON)
)

-- parent is a tree
CREATE TABLE [test].[Parent] (
    [ParentId] BIGINT NOT NULL,
    [ParentPid] BIGINT DEFAULT NULL,
    FOREIGN KEY([ParentPid]) REFERENCES [test].[Parent] ([ParentId]),
    CONSTRAINT [PK_Parent] PRIMARY KEY CLUSTERED ([ParentId]) WITH (IGNORE_DUP_KEY = ON)
)

-- each child can have any number of parents
CREATE TABLE [test].[ChildParent] (
    [ChildId] BIGINT NOT NULL,
    FOREIGN KEY([ChildId]) REFERENCES [test].[Child] ([ChildId]) ON DELETE CASCADE,
    [ParentId] BIGINT NOT NULL,
    FOREIGN KEY([ParentId]) REFERENCES [test].[Parent] ([ParentId]) ON DELETE CASCADE,
    CONSTRAINT [PK_ChildParent] PRIMARY KEY CLUSTERED ([ChildId], [ParentId]) WITH (IGNORE_DUP_KEY = ON)
)

-- () This table is internal and used readonly, generated by a trigger on ChildParent
-- that creates associations between each Child & Parent + all the Parent's Parents
-- this way flatteting the Parent structure and making deep querying easier.
-- () ChildId + ParentPid point directly to the original Child + Parent relationship
-- that when it's deleted, it automatically deletes all the Child + Parent's Parents.
-- () I also need the table to automagically delete any row when any Child/Parent's gone.
CREATE TABLE [test].[Parent_Child] (
    [ParentId] BIGINT NOT NULL,
    FOREIGN KEY([ParentId]) REFERENCES [test].[Parent] ([ParentId]) ON DELETE CASCADE,
    [ChildId] BIGINT NOT NULL,
    FOREIGN KEY([ChildId]) REFERENCES [test].[Child] ([ChildId]) ON DELETE CASCADE,
    [ParentPid] BIGINT NOT NULL,
    FOREIGN KEY([ParentPid]) REFERENCES [test].[Parent] ([ParentId]) ON DELETE CASCADE,
    FOREIGN KEY([ChildId], [ParentPid]) REFERENCES [test].[ChildParent] ([ChildId], [ParentId]) ON DELETE CASCADE,
    CONSTRAINT [PK_Parent_Child] PRIMARY KEY CLUSTERED ([ParentId], [ChildId], [ParentPid]) WITH (IGNORE_DUP_KEY = ON)
)

COMMIT TRANSACTION

最后一张桌子不会创建I know why，即使我根本不同意，因为我无法看到这个确切的场景如何破坏任何东西或做任何事情SQLServer很难。 MySQL做了（或者至少在我上次使用它之前做了1年）这没有问题。

我也知道我在上面的（非法SQL）中做出的任何改变（删除DELETE CASCADE，删除FOREIGN KEYS）将迫使我做清理客户端(C#)并打破我设计整齐的数据库。

考虑到我希望保留所有Parent_Child维护SQLServer端，以便C＃客户端只读取它，是否有针对这种情况的解决方法？

PS： 考虑使用INSTEAD OF DELETE触发器，但doc说你不能在{{1}的表上使用它}。

错误： 可能会导致循环或多个级联路径。指定ON DELETE NO ACTION或ON UPDATE NO ACTION，或修改其他FOREIGN KEY约束。。

Answer 1

我设法为这种情况创建了一种解决方法，而没有在客户端做任何工作：

创建了一个新表格，我在Parent上使用触发器展平整个父级层次结构。
使用此新表查询只是与我原始设计的连接，但不是递归。

表格结构：

CREATE TABLE [test].[ParentTree]
(
    [ParentId] BIGINT NOT NULL, -- no fkey, but I double the value on column 2 so no need
    [ParentPid] BIGINT NOT NULL,
    FOREIGN KEY([ParentPid]) REFERENCES [dbo].[Parent] ([ParentId]) ON DELETE CASCADE,
    CONSTRAINT [PK_ParentTree] PRIMARY KEY CLUSTERED ([ParentId], [ParentPid]) WITH (IGNORE_DUP_KEY = ON)
)
GO

因此，通过Parent上的触发器，递归CTE函数和OUTER APPLY来实现平面层次结构，以对Parents使用该函数。如果我有'z' 'y'孩子'x'的孩子，那么我的公寓桌子包含：

[Child] [Parent]
x x -- notice child is parent of child
y y -- notice child is parent of child
y x
z z -- notice child is parent of child
z y
z x

这允许我对平面数据集进行深度查询。我也可以在第2列有DELETE CASCADE，因为我将子值加倍，所以我可以避免使用双fkeys。

要查询[Child] [Parent] 中的所有X（包括Y的{{1}}和Z {}}中的所有{/ 1}}

我甚至可能进一步降低复杂性，但这是我对fkey级联混乱的解决方法。

PS ：复制一个fkey（所以我只能拥有一个）可能也适用于原始设计，但我对这个解决方案没问题，所以我不会尝试改变原始代码就像这样工作。

SQLServer两个外键指向同一列

1 个答案: