我可以从自引用（分层）表中获取树结构吗？

Question

给定一个这样的分层表：

CREATE TABLE [dbo].[btree]
(
  id INT PRIMARY KEY
, parent_id INT REFERENCES [dbo].[btree] ([id])
, name NVARCHAR(20)
);

我想获得整个树结构。

例如，使用此数据：

INSERT INTO [btree] VALUES (1, null, '1 Root');
INSERT INTO [btree] VALUES (2,    1, '1.1 Group');
INSERT INTO [btree] VALUES (3,    1, '1.2 Group');
INSERT INTO [btree] VALUES (4,    2, '1.1.1 Group');
INSERT INTO [btree] VALUES (5,    2, '1.1.2 Group');
INSERT INTO [btree] VALUES (6,    3, '1.2.1 Group');
INSERT INTO [btree] VALUES (7,    3, '1.2.2 Group');
INSERT INTO [btree] VALUES (8,    4, '1.1.1.1 Items');
INSERT INTO [btree] VALUES (9,    4, '1.1.1.2 Items');
INSERT INTO [btree] VALUES (10,   5, '1.1.2.1 Items');
INSERT INTO [btree] VALUES (11,   5, '1.1.1.2 Items');
INSERT INTO [btree] VALUES (12,   6, '1.2.1.1 Items');
INSERT INTO [btree] VALUES (13,   6, '1.2.1.2 Items');
INSERT INTO [btree] VALUES (14,   7, '1.2.2.1 Items');

我想获得：

+----+-----------+---------------------+
| id | parent_id | description         |
+----+-----------+---------------------+
|  1 |    NULL   | 1 Root              |
|  2 |     1     |   1.1 Group         |
|  4 |     2     |     1.1.1 Group     |
|  8 |     4     |       1.1.1.1 Items |
|  9 |     4     |       1.1.1.2 Items |
|  5 |     2     |     1.1.2 Group     |
| 10 |     5     |       1.1.2.1 Items |
| 11 |     5     |       1.1.2.2 Items |
|  3 |     1     |   1.2 Group         |
|  6 |     3     |     1.2.1 Group     |
| 12 |     6     |       1.2.1.1 Items |
| 13 |     6     |       1.2.1.2 Items |
|  7 |     3     |     1.2.2 Group     |
| 14 |     7     |       1.2.2.1 Items |
+----+-----------+---------------------+

我正在使用这样的递归查询获取记录：

;WITH tree AS
(
    SELECT c1.id, c1.parent_id, c1.name, [level] = 1
    FROM dbo.[btree] c1
    WHERE c1.parent_id IS NULL
    UNION ALL
    SELECT c2.id, c2.parent_id, c2.name, [level] = tree.[level] + 1
    FROM dbo.[btree] c2 INNER JOIN tree ON tree.id = c2.parent_id
)
SELECT tree.level, tree.id, parent_id, REPLICATE('  ', tree.level - 1) + tree.name AS description
FROM tree
OPTION (MAXRECURSION 0)
;

这是当前的结果：

+----+-----------+---------------------+
| id | parent_id | description         |
|  1 |    NULL   | 1 Root              |
|  2 |     1     |   1.1 Group         |
|  3 |     1     |   1.2 Group         |
|  6 |     3     |     1.2.1 Group     |
|  7 |     3     |     1.2.2 Group     |
| 14 |     7     |       1.2.2.1 Items |
| 12 |     6     |       1.2.1.1 Items |
| 13 |     6     |       1.2.1.2 Items |
|  4 |     2     |     1.1.1 Group     |
|  5 |     2     |     1.1.2 Group     |
| 10 |     5     |       1.1.2.1 Items |
| 11 |     5     |       1.1.1.2 Items |
|  8 |     4     |       1.1.1.1 Items |
|  9 |     4     |       1.1.1.2 Items |
+----+-----------+---------------------+

我不知道如何按级别排序。

有没有办法为每个子级别设置等级？

我设置了一个 Rextester

Answer 1

添加“路径”字段并按类似于文件路径的方式排序。正如 ypercube 所提到的，在这个例子中排序过于简单，恰好可以工作，但为了简单起见，我将保持原样。大多数情况下，当我使用这种模式时，我还是按名称而不是 ID 进行排序。

IF OBJECT_ID('[dbo].[btree]', 'U') IS NOT NULL 
    DROP TABLE [dbo].[btree];
GO

CREATE TABLE [dbo].[btree]
(
  id INT PRIMARY KEY
, parent_id INT REFERENCES [dbo].[btree] ([id])
, name NVARCHAR(20)
);
GO

INSERT INTO [btree] VALUES (1, null, '1 Root');
INSERT INTO [btree] VALUES (2,    1, '1.1 Group');
INSERT INTO [btree] VALUES (3,    1, '1.2 Group');
INSERT INTO [btree] VALUES (4,    2, '1.1.1 Group');
INSERT INTO [btree] VALUES (5,    2, '1.1.2 Group');
INSERT INTO [btree] VALUES (6,    3, '1.2.1 Group');
INSERT INTO [btree] VALUES (7,    3, '1.2.2 Group');
INSERT INTO [btree] VALUES (8,    4, '1.1.1.1 Items');
INSERT INTO [btree] VALUES (9,    4, '1.1.1.2 Items');
INSERT INTO [btree] VALUES (10,   5, '1.1.2.1 Items');
INSERT INTO [btree] VALUES (11,   5, '1.1.2.2 Items');
INSERT INTO [btree] VALUES (12,   6, '1.2.1.1 Items');
INSERT INTO [btree] VALUES (13,   6, '1.2.1.2 Items');
INSERT INTO [btree] VALUES (14,   7, '1.2.2.1 Items');

;WITH tree AS
(
    SELECT c1.id, c1.parent_id, c1.name, [level] = 1, path = cast('root' as varchar(100))
    FROM dbo.[btree] c1
    WHERE c1.parent_id IS NULL
    UNION ALL
    SELECT c2.id, c2.parent_id, c2.name, [level] = tree.[level] + 1, 
           Path = Cast(tree.path+'/'+right('000000000' + cast(c2.id as varchar(10)),10) as varchar(100))
    FROM dbo.[btree] c2 INNER JOIN tree ON tree.id = c2.parent_id
)
SELECT tree.path, tree.id, parent_id, REPLICATE('  ', tree.level - 1) + tree.name AS description
FROM tree
Order by path
OPTION (MAXRECURSION 0)
;

这里有一个雷克斯特