Question

我对SQL Server有疑问：如何根据下表数据获取所需的输出？

表格：parent

CREATE TABLE [dbo].[parent]
(
    [parentsupplierid] [int] NULL,
    [supplierid] [int] NULL,
    [suppliername] [varchar](50) NULL
) ON [PRIMARY]
GO

INSERT [dbo].[parent] ([parentsupplierid], [supplierid], [suppliername]) 
VALUES (123, 321, N'AAA'), (123, 231, N'BBB'),
       (NULL, 123, N'ABC'), (456, 654, N'DDD'),
       (NULL, 546, N'EEE'), (NULL, 456, N'DEF'),
       (789, 987, N'GGG'), (NULL, 879, N'HHH'),
       (NULL, 789, N'GHI')

基于上述数据，我希望输出如下：

parentsupplierid | supplierid | suppliername | PARENTsuppliername
-----------------+------------+--------------+-----------------
123              | 231        | BBB          |  ABC
123              | 321        | AAA          |  ABC
456              | 654        | DDD          |  DEF
456              | 546        | EEE          |  DEF
789              | 987        | GGG          |  GHI
789              | 879        | HHH          |  GHI

我这样尝试过：

SELECT DISTINCT  
    ISNULL( a.[parentsupplierid],b.[supplierid]) [parentsupplierid],
    --A.[parentsupplierid]
    A.[supplierid],
    A.[suppliername],
    B.[suppliername] AS [PARENTsuppliername]
FROM   
    [whatsup].[dbo].[parent] A 
LEFT JOIN 
    (SELECT  
         [parentsupplierid],
         [supplierid], 
         [suppliername]
     FROM 
         [whatsup].[dbo].[parent]
     WHERE 
         [parentsupplierid] IS NULL) B ON A.parentsupplierid = B.supplierid

此查询未返回预期结果。

请告诉我如何编写查询以在SQL Server中完成此任务。

Answer 1

这里有一段逻辑：“如果[当前记录]。[ParentSupplierId]为空且[先前记录]。[ParentSupplierId]为空，那么[当前记录]。[ParentSupplierId] = [先前记录]。[ SupplierId]”。

但是，除非您使用ORDER BY子句，否则不会按插入的顺序返回SQL记录，并且不指定返回的行顺序。最简单的方法是将ID字段添加到表中，并将其用于[Previous Record]，如下所示：

CREATE TABLE [dbo].[parent]
(
    [parentId] int IDENTITY(1,1),
    [parentsupplierid] [int] NULL,
    [supplierid] [int] NULL,
    [suppliername] [varchar](50) NULL
) ON [PRIMARY]
GO

INSERT [dbo].[parent] ([parentsupplierid], [supplierid], [suppliername]) 
VALUES (123, 321, N'AAA'), (123, 231, N'BBB'),
       (NULL, 123, N'ABC'), (456, 654, N'DDD'),
       (NULL, 546, N'EEE'), (NULL, 456, N'DEF'),
       (789, 987, N'GGG'), (NULL, 879, N'HHH'),
       (NULL, 789, N'GHI')

然后使用您的基本逻辑找到正确的父母，请尝试：

SELECT DISTINCT  
    ISNULL( a.[parentsupplierid],b.[supplierid]) [parentsupplierid],
    --A.[parentsupplierid]
    A.[supplierid],
    A.[suppliername],
    B.[suppliername] AS [PARENTsuppliername]
FROM   
    [whatsup].[dbo].[parent] A  --- Table for base records
LEFT JOIN [whatsup].[dbo].[parent] M  -- Join for missing parent
    ON M.[parentId] = (A.[parentId] - 1)
    AND M.[parentsupplierid] IS NULL
    AND A.[parentsupplierid] IS NULL
INNER JOIN [whatsup].[dbo].[parent] B
    ON ISNULL(A.parentsupplierid, M.supplierId) = B.supplierid

如何在SQL Server中获得预期的输出

1 个答案: