sql-server - 在 SQL 中获取两个值中的较大者

Question

我有一个 SQL Server 表。此表有两个表：Order 和 OrderInProgress。这两个表具有相似的结构：

Order[InProgress]
-----------------
ID (uniqueidentifier)
CreateDate
...

我需要获取最新的 Order 或 OrderInProgress

DECLARE @latestOrderID uniqueidentifier
@latestOrderID = ?

如何将 @latestOrderID 设置为最新的 Order 或 OrderInProgress ID？我无法弄清楚如何在 SQL 中执行此操作。

谢谢！

Answer 1

Try this, which should be more efficient whenever it matters.

   select top 1 ID from (
        select top 1 ID from Order order by ID desc
      union all
        select top 1 ID from OrderInProgress order by ID desc
    ) T
    order by ID desc

Answer 2

你有没有尝试过：

SELECT TOP 1 @latestOrderID = ID FROM [Order] ORDER BY CreateDate DESC

Answer 3

SELECT * FROM
(SELECT 'Order' tablename, max(ID) max_id FROM Order
UNION
SELECT 'OrderInProgress' tablename, max(ID) max_id FROM OrderInProgress
) maxes ORDER BY max_id DESC