在 SQL 服务器视图中插入重复行

Question

我想知道是否可以在 SQL Server 2008 R2 中创建仅包含最后一列 (DateTime DESC) 的视图，但最后一行应该再次复制到视图中。

因此最终结果将是一个包含两行数据相同的视图。

select一行的查询很简单：

SELECT TOP 1 * 
FROM Reporting
ORDER BY DateTime DESC

或

SELECT TOP 1 *
FROM Reporting
WHERE DateTime IN (SELECT MAX(DateTime) 
                   FROM Reporting)

这returns只有一行，但我想在视图中再次复制这一行。

谢谢

Answer 1

尝试联合所有：

SELECT TOP 1 * FROM Reporting ORDER BY DateTime DESC 
UNION ALL
SELECT TOP 1 * FROM Reporting ORDER BY DateTime DESC

Answer 2

上述答案中的语法无效。 UNION ALL 中的每个数据源中不允许有 ORDER BY。你只能在最后陈述中有一个。所以，这是错误的：

SELECT TOP 1 * FROM Reporting ORDER BY DateTime DESC 
UNION ALL
SELECT TOP 1 * FROM Reporting ORDER BY DateTime DESC

并且应该这样做：

SELECT * FROM (SELECT TOP 1 * FROM Reporting ORDER BY DateTime DESC)
UNION ALL
SELECT * FROM (SELECT TOP 1 * FROM Reporting ORDER BY DateTime DESC);

我会建议使用不同的方法。使用假数据源然后 cross apply.

SELECT SI.*
FROM
(
    SELECT 1
    UNION ALL
    SELECT 2
) DS ([col])
CROSS APPLY
(

    SELECT TOP 1 * FROM Reporting ORDER BY DateTime DESC
) SI;

您可以轻松地测试此语句的执行计划更好，只导致一次排序和索引扫描：

Insert duplicate row in SQL Server view