sql-server - SQL Server : implicit data type conversions chart

Question

据我所知，根据this chart ，从 VARBINARY 到 DATE 的隐式转换应该没问题。但是，当我尝试以下代码时，SQL Server 响应“不允许从数据类型 varbinary(max) 到 date 的隐式转换。请使用 CONVERT 函数运行此查询。”

CREATE TABLE [dbo].[CONVERSION_TEST](
[mydate] [date] NULL
) ON [PRIMARY]

GO


declare @bin varbinary(MAX) = NULL
insert into conversion_test values (@bin)

我在 SQL Server 2012(版本 11.0.3128)上运行此程序。

Answer 1

刚刚找到这个连接帖子:

Microsoft Connect

其中有来自 Microsoft 的以下声明:

Posted by Microsoft on 05/03/2008 at 13:23 After some serious discussion, we believe that the current design is good especially given it's not an interesting scenario and we already support explicit conversion for the new date/time types.

On the other hand, we also think that it's not necessarily a good thing given we supported too many implicit conversions on existing types. Conversion to/from binary is a dangerous thing, and requiring explicit conversion makes sense. It's unfortunate that ALTER TABLE behavior is tied to implicit conversion, but you can always work around it by creating a new column, issue an update, and then drop old column if that's main scenario you worried.

So if no strong objection, we're going to do the followings: - Fixing the BOL to indicate that there's no implicit conversion support from binary/varbinary to new date/time types - Close this as 'By Design'

thanks

因此，他们似乎决定禁止这种隐式转换，但不更新该图表。