sql-server - 如何使用公用表表达式在 SQL Server 中进行分层排序

Question

可能重复：
使用 CTE 进行真正的递归？

给定一个引用自身的分层表，例如具有以下列的 Employee 表：

Table      Employee
    Column Id INT NOT NULL
    Column ParentId INT NOT NULL (references Id)
    Column Name NVARCHAR(60) NOT NULL

以下查询将为我提供基于给定 EmployeeId 的所有记录：

DECLARE @EmployeeId INT = <%insert EmployeeId here%>;

WITH CDE AS
(
    SELECT
        *,
        0 AS Level
    FROM
        collaboration.Employee AS E
    WHERE
        Id = @EmployeeId
    UNION ALL
    SELECT
        E.*,
        CDE.Level + 1 AS Level
    FROM
        collaboration.Employee AS E
        INNER JOIN
        CDE ON E.ParentId = CDE.Id AND E.Id <> 0
)
SELECT DISTINCT
    CDE.*
FROM
    CDE
ORDER BY
    CDE.Level

如果有意义的话，我想要的是能够按“分支”然后“级别”进行排序。所以给出下表：

1    0    John Smith
2    1    John Doe
3    1    Jane Williams
4    2    Ian Bond
5    2    James Fleming

我希望结果看起来像：

1    0    John Smith
2    1    John Doe
4    2    Ian Bond
5    2    James Fleming
3    1    Jane Williams

我想要一个不涉及构建字符串以方便排序的解决方案。如果无法解决，我想知道原因。

Answer 1

;WITH CDE AS 
( 
    SELECT 
        *, 
        0 AS Level,
        convert(nvarchar(50),id) as EPath
    FROM 
        collaboration.Employee AS E 
    WHERE 
        Id = @EmployeeId 
    UNION ALL 
    SELECT 
        E.*, 
        CDE.Level + 1 AS Level ,
        convert(nvarchar(50),Epath+'/'+CONVERT(nvarchar(5),e.id))
    FROM 
        collaboration.Employee AS E 
        INNER JOIN 
        CDE ON E.ParentId = CDE.Id AND E.Id <> 0 
) 
SELECT DISTINCT 
    CDE.* 
FROM 
    CDE 
ORDER BY 
    EPath

By the way, SQL Server 2008 has a HierarchyID data type for just this kind of thing.