Question

我在数据库中保存了虚拟文件夹结构，我想从当前文件夹到根目录获取面包屑。数据可以是未分类的（但最好是排序），我只想要当前文件夹的父文件夹。

表定义是：

DECLARE Folders TABLE (
    FOL_PK INT IDENTITY(1,1) NOT NULL,
    FOL_Name VARCHAR(200) NOT NULL,
    FOL_FOL_FK INT NULL -- Foreign key to parent
)

这是我的解决方案：

DECLARE @FOL_PK INT = 5 -- Current folder PK

DECLARE @breadcrumbs TABLE (
    FOL_PK INT NOT NULL,
    FOL_Name VARCHAR(200) NOT NULL,
    FOL_FOL_FK INT NULL
)

DECLARE @isRoot BIT = 0
       ,@currentFolderPK INT
       ,@parentFK INT

-- Get current and parent folder PK
SELECT
    @currentFolderPK = FOL_PK
FROM
    Folder
WHERE
    FOL_PK = @FOL_PK

-- Breadcrumb
WHILE (@isRoot = 0)
BEGIN
    -- Save to breadcrumb
    INSERT INTO @breadcrumbs
        SELECT
            FOL_PK,
            FOL_Name,
            FOL_FOL_FK
        FROM
            Folder
        WHERE
            FOL_PK = @currentFolderPK

    -- Set parent as current
    SET @currentFolderPK =
    (
        SELECT
            FOL_FOL_FK
        FROM
            Folder
        WHERE
            FOL_PK = @currentFolderPK
    )

    -- Set flag for loop
    SET @isRoot = CASE 
                     WHEN ISNULL(@currentFolderPK, 0) = 0 THEN 1 
                     ELSE 0 
                  END
END

-- Return breadcrumbs
SELECT
    FOL_PK AS PK,
    FOL_Name AS Name,
    FOL_FOL_FK AS ParentFK
FROM
    @breadcrumbs

问题是我对循环不太满意。有没有其他复杂的解决方案如何做到这一点？

Answer 1

使用递归公用表表达式（CTE）：

来尝试此操作

SQL Fiddle

MS SQL Server 2008架构设置：

CREATE TABLE [Folders](
    [FOL_PK] [int] IDENTITY(1,1) NOT NULL,
    [FOL_Name] [varchar](200) NOT NULL,
    [FOL_FOL_FK] [int] NULL,
 CONSTRAINT [PK__Folders__FOL_PK] PRIMARY KEY CLUSTERED 
(
    [FOL_PK] ASC
))

ALTER TABLE [dbo].[Folders]  
  WITH CHECK ADD  CONSTRAINT [FK_Folders_Folders] FOREIGN KEY([FOL_FOL_FK])
REFERENCES [dbo].[Folders] ([FOL_PK])

ALTER TABLE [dbo].[Folders] CHECK CONSTRAINT [FK_Folders_Folders]



INSERT INTO Folders(FOL_Name, FOL_FOL_FK)
VALUES ('Level 1', NULL),
       ('Level 1.1', 1),
       ('Level 1.2', 1),
       ('Level 1.3', 1),
       ('Level 1.2.1', 3),
       ('Level 1.2.2', 3),
       ('Level 1.2.3', 3),
       ('Level 1.2.2.1', 6),
       ('Level 1.2.2.2', 6),
       ('Level 1.2.2.3', 6),
       ('Level 1.3.1', 4),
       ('Level 1.3.2', 4)

查询1 ：

DECLARE @FolderId Int = 9

;WITH CTE
AS
(
    SELECT FOL_PK AS PK, FOL_NAME As Name, FOL_FOL_FK AS ParentFK
    FROM Folders
    WHERE FOL_PK = @FolderId
    UNION ALL
    SELECT F.FOL_PK AS PK, F.FOL_NAME AS Name, F.FOL_FOL_FK AS ParentFK
    FROM Folders F
    INNER JOIN CTE C
        ON C.ParentFK = F.FOL_PK

)
SELECT *
FROM CTE

<强> Results ：

| PK |          Name | ParentFK |
|----|---------------|----------|
|  9 | Level 1.2.2.2 |        6 |
|  6 |   Level 1.2.2 |        3 |
|  3 |     Level 1.2 |        1 |
|  1 |       Level 1 |   (null) |

T-SQL层次结构 - 使用查询获取面包屑

1 个答案: