Question

我有2张桌子：

DesignGroup表：

+--------------------------------------+--------+
|            DesignGroupId             |  Name  |
+--------------------------------------+--------+
| 9D32C543-24EA-497E-918E-387C8A66BF1A | Group1 |
| 532C543E-24EA-497E-918E-387C8A66BF1A | Group2 |
+--------------------------------------+--------+

设计表：

+-----------+---------------+--------------------------------------+
| DesignKey |     Name      |            DesignGroupId             |
+-----------+---------------+--------------------------------------+
|         1 | Design        | 9D32C543-24EA-497E-918E-387C8A66BF1A |
|         2 | Design        | 9D32C543-24EA-497E-918E-387C8A66BF1A |
|         3 | AnotherDesign | 532C543E-24EA-497E-918E-387C8A66BF1A |
+-----------+---------------+--------------------------------------+

如您所见，多个设计可以具有相同的DesignGroupId，所以我进行如下查询：

DECLARE @DesignName VARCHAR(255) = 'Design'

SELECT 
    [D].[Name] AS [Display],
    [D].[DesignKey] AS [Value]
FROM 
    [Design] AS [D]
JOIN 
    [DesignGroup] AS [DG] ON [D].[DesignGroupId] = [DG].[DesignGroupId]
GROUP BY
    [D].[Name], [D].[DesignKey];

我的愿望结果是，每个DesignGroupId仅获得一个值[Display]和一个[Value]，所以我的愿望结果是：

+---------------+-------+
|    Display    | Value |
+---------------+-------+
| Design        |     1 |
| AnotherDesign |     3 |
+---------------+-------+

但是我得到每个DesignKey的结果，如：

+---------------+-------+
|    Display    | Value |
+---------------+-------+
| Design        |     1 |
| Design        |     2 |
| AnotherDesign |     3 |
+---------------+-------+

我该如何解决？问候

Answer 1

我不明白为什么需要加入表格。
您想要的结果仅取决于表[Design]中的数据。
因此GROUP BY [Name]并获得[DesignKey]的最小值：

SELECT 
    [Name] AS [Display],
    MIN([DesignKey]) AS [Value]
FROM [Design]
GROUP BY [Name];

但是如果表中的DesignGroupId只有一个值，那就没问题了。
其他DesignGroupId所需要的结果是什么？
也许GROUP BY [DesignGroupId], [Name]：

SELECT 
    [DesignGroupId], 
    [Name] AS [Display],
    MIN([DesignKey]) AS [Value]
FROM [Design]
GROUP BY [DesignGroupId], [Name];

Answer 2

您的目标是获取每个名称（显示）和组的最小DesignKey值吗？您可以将结果包装到最小值外部查询中：

SELECT DISPLAY, MIN(VALUE) from (
SELECT 
    [D].[Name] AS [Display],
    [D].[DesignKey] AS [Value]
FROM 
    [Design] AS [D]
JOIN 
    [DesignGroup] AS [DG] ON [D].[DesignGroupId] = [DG].[DesignGroupId]
GROUP BY
    [D].[Name], [D].[DesignKey])
GROUP BY Display;

从关系中获取错误的数据

2 个答案: