SQL 树结构表

Question

我是 SQL 新手，希望得到有关以下问题的任何帮助。我有以下代码为节点和树创建表，但不确定如何在我的代码中实现以下规则。

create table Node(
    NodeId int not null,
    ParentId int null,
    NodeName varchar(255) not null,
    constraint PK_Node primary key(NodeId),
    constraint UK_NodeName unique(NodeName)
)
go

create table Tree(
    NodeId int not null,
    ParentId int not null,
    Level int not null,
    constraint PK_Tree primary key(NodeId, ParentId),
    constraint UK_Level unique(NodeId, Level)
)
go}

alter table Node
	add constraint FK_NodeNode foreign key(ParentId) references Node(NodeId) --on delete cascade;

alter table Tree
	add constraint FK_NodeTreeNode foreign key(NodeId) references Node(NodeId) on delete cascade;

想象一个具有以下属性的树结构：

• a) 单根节点
• b) 每个节点可能有多个子节点
• c) 不能删除节点
• d) 所有非根节点都有一个属性 max children nodes - 新节点默认为固定默认值
• e) 可以随时更改最大子节点属性 - 如果新值小于当前子节点数，则子节点将按照沿途所有节点的属性沿链向上分布。如果该属性设置为零，则该节点将成为根节点的直接子节点
• f) 添加新节点时，它会添加到尽可能接近根级别的节点，按填充的子节点百分比配额升序排列。如果所有节点都达到了配额，则将其直接置于根节点之下。

创建表和索引来存储这些信息和过程，以尽可能高效地执行以下操作：

• i.向树中添加节点
• 二。更改节点的最大子节点属性

Answer 1

并非所有约束都可以在 SQL Server 中设置。 a、d、e、f的逻辑应该在应用中迎合。

一棵树只是Nodes 的组合。所以我们只需要定义Node的存储。

create table Node(
    NodeId int not null identity(1,1), -- Identity, auto generate Id for new Node
    ParentId int null, -- If null, it is the root of the tree
    MaxChild int not null default(-1),
    NodeName varchar(255) not null,
    constraint PK_Node primary key(NodeId),
    constraint UK_NodeName unique(NodeName),
    constraint FK_Node foreign key(ParentId) references Node(NodeId) 
    -- How the `Node` to be related and form the tree can be done 
    -- by adding the `Foreign Key` of `Node` itself
    -- A node cannot be simply deleted if it is a parent.
)

添加节点：

-- Add root
insert Node (NodeName) VALUES ('root')

-- Add child
insert Node (ParentId, NodeName) VALUES 
((SELECT NodeId FROM Node WHERE NodeName = 'Root'), 'ChildA')

insert Node (ParentId, NodeName) VALUES 
((SELECT NodeId FROM Node WHERE NodeName = 'Root'), 'ChildB')

insert Node (ParentId, NodeName) VALUES 
((SELECT NodeId FROM Node WHERE NodeName = 'ChildA'), 'ChildA-A')

insert Node (ParentId, NodeName) VALUES 
((SELECT NodeId FROM Node WHERE NodeName = 'ChildA-A'), 'ChildA-A-A')

获取Nodes的级别和子级数

;WITH 
CountLevel AS
(
    SELECT *, 1 AS Level FROM Node WHERE ParentId IS NULL

    UNION ALL

    SELECT child.*, parent.Level + 1 
    FROM Node child INNER JOIN CountLevel parent ON 
        child.ParentId = parent.NodeId
), 
CountChild AS
(
    SELECT NodeId, ParentId, 0 AS ChildCount 
    FROM Node leaf 
    WHERE NOT EXISTS(SELECT * FROM Node WHERE ParentId = leaf.NodeId)

    UNION ALL

    SELECT child.ParentId, (SELECT ParentId FROM Node WHERE NodeId = child.ParentId), child.ChildCount + 1 
    FROM CountChild child
    WHERE child.ParentId IS NOT NULL
)
SELECT *, (SELECT SUM(ChildCount) FROM CountChild WHERE NodeId = CountLevel.NodeId) Child FROM CountLevel

结果

NodeId      ParentId    MaxChild    NodeName             Level       Child
----------- ----------- ----------- -------------------- ----------- -----------
1           NULL        -1          Root                 1           4
2           1           -1          ChildA               2           2
3           1           -1          ChildB               2           0
4           2           -1          ChildA-A             3           1
5           4           -1          ChildA-A-A           4           0