Sql 我怎样才能编写一个程序，从I到j或类似这样的树获取级别？

我有一张像这样的桌子

        Users
-------------------------
id | ancestor_id | ....
-------------------------
 1 |    NULL     | ....
 2 |     1       | ....
 3 |     1       | ....
 4 |     3       | ....
 5 |     3       | ....

那将代表一棵像树一样的树

   level 1           1
                   /  \ 
   level 2        2    3 
                      / \
   level 3           4   5

我想创建一个过程，返回给定用户的第I代到第j代后代：

CREATE PROCEDURE DescendantsLevel 
   @user_id INT,
   @i INT,
   @j INT
AS
   ....

但是，如果@j为NULL，它将返回从@i代开始的所有子代

示例：

会回来吗

-------------------------
id | ancestor_id | ....
-------------------------
 1 |    NULL     | ....
 2 |     1       | ....
 3 |     1       | ....
 4 |     3       | ....
 5 |     3       | ....

及

会回来吗

        Users
-------------------------
id | ancestor_id | ....
-------------------------
 1 |    NULL     | ....
 2 |     1       | ....
 3 |     1       | ....

我有几个问题：

在SQL中，有比NULL更好的值来表示无穷大的概念吗？ 我如何实现我描述的过程？ 是否有更好的数据库设计方法来简化过程？ 使用递归CTE：

DECLARE @test TABLE (id INT NOT NULL, ancestor_id INT NULL)

DECLARE
    @id INT = 1,
    @i INT = 1,
    @j INT = 2

INSERT INTO @test (id, ancestor_id)
VALUES
    (1, NULL),
    (2, 1),
    (3, 1),
    (4, 3),
    (5, 3)

;WITH CTE_Tree AS
(
    SELECT
        id,
        ancestor_id,
        1 AS lvl,
        id AS base
    FROM
        @test
    WHERE
        id = @id
    UNION ALL
    SELECT
        C.id,
        C.ancestor_id,
        P.lvl + 1 AS lvl,
        P.base AS base
    FROM
        CTE_Tree P
    INNER JOIN @test C ON C.ancestor_id = P.id
    WHERE
        lvl <= COALESCE(@j, 9999)
)
SELECT
    id,
    ancestor_id
FROM
    CTE_Tree
WHERE
    lvl BETWEEN @i AND COALESCE(@j, 9999)

---

这依赖于不超过9999个递归级别—实际上SQL Server的递归默认限制为100，因此超过100个级别时，您将得到一个错误。

Lookup recursive ctes。如果您使用此设计，这将是解决此问题的最简单方法。您还可以将嵌套集模型视为邻接列表的更好替代方案。如果在第一个示例中@i为2，那么为什么返回id 1？为什么不添加级别列？使查询变得非常简单。添加级别列会将手动计算的列添加到表中-这会增加复杂性，然后可能会失去同步并导致其他问题。

        Users
-------------------------
id | ancestor_id | ....
-------------------------
 1 |    NULL     | ....
 2 |     1       | ....
 3 |     1       | ....

DECLARE @test TABLE (id INT NOT NULL, ancestor_id INT NULL)

DECLARE
    @id INT = 1,
    @i INT = 1,
    @j INT = 2

INSERT INTO @test (id, ancestor_id)
VALUES
    (1, NULL),
    (2, 1),
    (3, 1),
    (4, 3),
    (5, 3)

;WITH CTE_Tree AS
(
    SELECT
        id,
        ancestor_id,
        1 AS lvl,
        id AS base
    FROM
        @test
    WHERE
        id = @id
    UNION ALL
    SELECT
        C.id,
        C.ancestor_id,
        P.lvl + 1 AS lvl,
        P.base AS base
    FROM
        CTE_Tree P
    INNER JOIN @test C ON C.ancestor_id = P.id
    WHERE
        lvl <= COALESCE(@j, 9999)
)
SELECT
    id,
    ancestor_id
FROM
    CTE_Tree
WHERE
    lvl BETWEEN @i AND COALESCE(@j, 9999)