SQL Server 递归最大级别

Question

我在 SQL 2008 中有一个基本的递归表设置，其结构如下：

CREATE TABLE [dbo].[Employee]
(
[Id] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](100) NOT NULL,
[ManagerId] [int] NULL,
CONSTRAINT [PK_Employee] PRIMARY KEY CLUSTERED ([Id] ASC)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

ALTER TABLE [dbo].[Employee]  WITH CHECK ADD  CONSTRAINT [FK_Employee_Employee] FOREIGN KEY([ManagerId]) REFERENCES [dbo].[Employee] ([Id])

根据网上几篇不同的文章，我找到了可以编写如下查询的地方，以返回“经理”和下面包含的所有子记录：

WITH DirectRelationships AS
(
SELECT Id, Name, ManagerId, Depth = 0
FROM Employee
WHERE ManagerId = 1
UNION ALL
SELECT e.Id, e.Name, e.ManagerId, Depth = Depth + 1
FROM Employee e
INNER JOIN DirectRelationships DR ON DR.Id = e.ManagerId
WHERE Depth <= 2 /* this doesn't work */
)
SELECT * FROM DirectRelationships

当我在没有“WHERE Depth

例如，假设我在此表中有以下数据：

select * from Employee;

Id  | Name             | ManagerId | Depth
------------------------------------------
1    CEO                 0           0
2    National Director   1           1
3    Regional Director   2           2
4    Store Director      3           3
5    Clerk               4           4
6    Clerk #2            4           4

我希望我的查询能够做的是获得经理级别（例如，国家主管或 ID #2）并指定要递归提取的级别数（例如，2）。这将返回以下内容：

Id  | Name             | ManagerId | Depth
------------------------------------------
2    National Director   1           0 /*top level requested */
3    Regional Director   2           1 /*new depth based on requested parent */
4    Store Director      3           2 /*new depth based on requested parent */

所以我不会得到最高级别的 CEO 职位，我也不会得到个人文员，因为我只想要一个特定的条目和低于它的 2 个级别。我已经看到您可以在查询中指定 MAXRECURSION 的位置，但是如果级别超过您指定的不可取的数字，则会引发错误。我将要处理的层次结构可能有数千条记录，对于任何特定的实体列表，我只需要最多 5 个子级别，而其他级别无关紧要。

任何帮助将不胜感激！

Answer 1

尝试运行：

WITH DirectRelationships AS
(
    SELECT Id, Name, ManagerId, Depth = 0
    FROM Employee
    WHERE Id = 2

    UNION ALL

    SELECT e.Id, e.Name, e.ManagerId, Depth = Depth + 1
    FROM Employee e
        INNER JOIN DirectRelationships DR ON DR.Id = e.ManagerId
)
SELECT * 
FROM DirectRelationships 
WHERE Depth <= 2

你应该得到你正在寻找的结果：

Id Name              ManagerId Depth
-- ----------------- --------- -----
2  National Director 1         0
3  Regional Director 2         1
4  Store Director    3         2