获取多层次项的 SQL 查询答案

【问题标题】：SQL query to get multihierarchy items获取多层次项的 SQL 查询
【发布时间】：2015-11-12 14:58:38
【问题描述】：

在我的 SQL 表中，我有以下数据

ID  Level   Description     Code    MasterID
1   1       Cars            AD0       NULL
2   1       Trucks          JF1       NULL
3   1       Items           YU2       NULL
4   2       New Cars        AS3        1
5   2       Used Cars       TG4        1
6   2       Car parts       UJ5        1
7   2       New trucks      OL6        2
8   2       Used trucks     PL7        2
9   2       Truck parts     KJL8       2
10  2       Factory stuff   UY9        3
11  2       Custom stuff    RT10       3
12  3       Toyota          6YH11      4
13  3       BMW             9OKH12     4
14  3       VW              13         5
15  3       Tiers Type I    J14        6
16  3       Tiers Type II   J15        6
17  3       Tiers Type III  ADS16      9
18  3       Seats           SA17       6
19  3       Doors           UU18       6
20  3       Lights          9OL19      6
21  4       Left light      GH20       20
22  4       Right light     H21        20
23  4       Left door       JHJ22      19
24  4       Michelin        UY23       16
25  4       Vredestein      GTF24      17
26  4       Dunlop          25         15

我的成就是获取每个项目的所有层次结构数据。例如，输出应如下所示

ID  Level   Description   Code   MasterId1   Description1     MasterId2   Description2    MasterId3    Description3

24   4       Michelin     UY23       16      Tiers Type II       6         Car Parts           1        Cars
.
.
19   3       Doors        UU18       6       Car Parts           1          Cars               NULL      NULL
.
.
10   2       Factory Stuff UY9       3       Items               NULL     NULL                 NULL     NULL
.
.
3    1        Items        NULL      NULL     NULL               NULL     NULL                 NULL     NULL
.
.

如果有人可以提供帮助或建议如何实现这一目标？

【问题讨论】：

你能告诉我们你到目前为止做了什么吗？
一般是CTE would do the trick in this scenario。我建议你从这里开始，也看看UNPIVOT，然后是动态SQL，然后想办法将它们组合在一起。但这一切都取决于您使用的 RDBMS。
关卡数量是否有上限？

标签： sql hierarchy multi-level

【解决方案1】：

这不是动态的，但很容易。

使用递归 cte，您可以获得整个表的层次结构，并通过几次自连接来获得您想要的表结构。

;WITH cte AS 
(
    SELECT *, ID AS [RootID], 1 AS [MasterLevel] FROM Table1
    UNION ALL
    SELECT t1.*, cte.[RootID], cte.[MasterLevel] + 1  FROM Table1 t1
    JOIN cte ON t1.ID = cte.MasterID  
)
SELECT  r.ID, r.[Level], r.[Description], r.[Code],
        m1.ID AS MasterId1, m1.[Description] AS Description1, 
        m2.ID AS MasterId2, m1.[Description] AS Description2,
        m3.ID AS MasterId3, m1.[Description] AS Description3
FROM    cte r
        LEFT JOIN cte m1 ON m1.[RootID] = r.[RootID] AND m1.MasterLevel = 2
        LEFT JOIN cte m2 ON m2.[RootID] = r.[RootID] AND m2.MasterLevel = 3
        LEFT JOIN cte m3 ON m3.[RootID] = r.[RootID] AND m3.MasterLevel = 4
WHERE   r.MasterLevel = 1
ORDER BY r.RootID DESC, r.MasterLevel

这将构建一个动态 sql 以根据最大 Level 值获取主字段和描述字段。或者您可以通过更改@MaxLevel 来定义您想要查看的级别

DECLARE @Sql VARCHAR(MAX) = '',
        @SelectSql VARCHAR(MAX) = '',
        @JoinSql VARCHAR(MAX) = '',
        @MaxLevel INT,
        @idx INT = 1

SET @MaxLevel = (SELECT MAX([Level]) FROM Table1)
WHILE @idx < @MaxLevel
BEGIN
    SET @SelectSql = @SelectSql + REPLACE(', m<index>.ID AS MasterId<index>, m<index>.[Description] AS Description<index> ', '<index>', @idx)
    SET @JoinSql = @JoinSql + REPLACE(' LEFT JOIN cte m<index> ON m<index>.[RootID] = r.[RootID] AND m<index>.MasterLevel = <index> ', '<index>', @idx)
    SET @idx = @idx + 1
END        
SET @Sql = '
    ;WITH cte AS 
    (
        SELECT *, ID AS [RootID], 0 AS [MasterLevel] FROM Table1
        UNION ALL
        SELECT t1.*, cte.[RootID], cte.[MasterLevel] + 1  FROM Table1 t1
        JOIN cte ON t1.ID = cte.MasterID  
    )
    SELECT  r.ID, r.[Level], r.[Description], r.[Code]' + @SelectSql
    + 'FROM cte r ' + @JoinSql
    + 'WHERE    r.MasterLevel = 0
    ORDER BY r.RootID DESC, r.MasterLevel'

EXEC(@Sql)

【讨论】：