SQL Server 中的家谱树

Question

在我的表中，每条记录都有一个指向其直接父级的指针，我需要知道如何查询给定记录的所有后代，无论是直系还是非直系（儿子的儿子）。

事实：

• 我不知道树有多深，我需要所有的叶子
• 某些记录可能没有子记录
• 我在 SqlServer 2012 下运行

谁能告诉我如何编写这样的查询？

Answer 1

对我来说，使用 CTE 进行递归似乎是最简单的方法，这是一个示例...

DECLARE @people TABLE
(
    Id INT,
    Name NVARCHAR(50),
    ParentId INT
)

INSERT INTO @people (Id, Name, ParentId) VALUES (1, 'Abigail', null)
INSERT INTO @people (Id, Name, ParentId) VALUES (2, 'Ben', 5)
INSERT INTO @people (Id, Name, ParentId) VALUES (3, 'Charlie', 2)
INSERT INTO @people (Id, Name, ParentId) VALUES (4, 'Dave', 1)
INSERT INTO @people (Id, Name, ParentId) VALUES (5, 'Ed', 6)
INSERT INTO @people (Id, Name, ParentId) VALUES (6, 'Frank', null)

;WITH ancestors AS (
 SELECT Id, Name, ParentId FROM @people WHERE Id = 3 
 UNION ALL
 SELECT p.Id, p.Name, p.parentId FROM @people p
 INNER JOIN ancestors a ON a.parentId = p.Id --This inner join causes the recurrsion
)
SELECT Id, Name, ParentId FROM ancestors

要从子代到祖先，将 ON 语句切换为另一种方式：

DECLARE @people TABLE
(
    Id INT,
    Name NVARCHAR(50),
    ParentId INT
)

INSERT INTO @people (Id, Name, ParentId) VALUES (1, 'Abigail', null)
INSERT INTO @people (Id, Name, ParentId) VALUES (2, 'Ben', 5)
INSERT INTO @people (Id, Name, ParentId) VALUES (3, 'Charlie', 2)
INSERT INTO @people (Id, Name, ParentId) VALUES (4, 'Dave', 1)
INSERT INTO @people (Id, Name, ParentId) VALUES (5, 'Ed', 6)
INSERT INTO @people (Id, Name, ParentId) VALUES (6, 'Frank', null)

;WITH ancestors AS (
 SELECT Id, Name, ParentId FROM @people WHERE Id = 6
 UNION ALL
 SELECT p.Id, p.Name, p.parentId FROM @people p
 --INNER JOIN ancestors a ON a.parentId = p.Id --It was this to go down...
   INNER JOIN ancestors a ON a.Id = p.parentId --Now use this to go up the tree
)
SELECT Id, Name, ParentId FROM ancestors

Answer 2

基于 Josh Wallace 的查询，获取后代。

declare @people table
(
    Id int,
    Name nvarchar(50),
    ParentId int
)

insert into @people values (1, 'Frank', null)
insert into @people values (2, 'Shane', null)
insert into @people values (3, 'George', 1)
insert into @people values (5, 'Hank', 1)
insert into @people values (7, 'Abigail', 3)
insert into @people values (8, 'Ben', 3)
insert into @people values (9, 'Charlie', 5)
insert into @people values (10, 'Dave', 5)
insert into @people values (11, 'Homer', 5)
insert into @people values (12, 'Junebug', 7)
insert into @people values (13, 'Bart', 11)
insert into @people values (14, 'Lisa', 11)


;with descendents AS (
    -- Anchor member definition
    select p.Id, p.Name, p.ParentId, Level = 0 
    from @people p 
    where p.Id = 1 -- person to search for descendents 

    union all

    -- Recursive member definition
    select p.Id, p.Name, p.ParentId, Level + 1
    from @people p 
    inner join descendents a on p.ParentId = a.Id
)


select 
    a.Level, ParentID = p.Id, Parent = p.Name, a.Id, Child = a.Name
from descendents a 
    left join @people p on p.Id = a.ParentId
order by a.Level