SQL Server将时间戳数据类型转换为十进制

Question

试图解决这个问题,根据MSDN上的Cast和Convert文档,这应该是可能的( http://msdn.microsoft.com/en-us/library/ms187928.aspx)

看看转换表.

我正在运行以下代码:

CREATE TABLE TableName (
    ID bigint Identity(1,1),
    SomeValue nvarchar(20) not null,
    TimestampColumn timestamp not null)

Insert Into TableName (SomeValue)
values ('testing')

SELECT Convert(decimal, TimeStampColumn) from TableName

但是我只是得到以下错误:

将数据类型时间戳转换为数字时出错.

根据文档应该是可能的,还是我遗漏了什么？注意我还需要转换回相同的时间戳值.

SELECT TimeStampColumn, Convert(timestamp, Convert(decimal, TimeStampColumn)) 
FROM TableName

最后,上面的查询应该呈现相同的值.

Answer 1

试试这个; 虽然MSDN说这是一个隐式转换,但它实际上不起作用.所以,我正在做的是将其转换为INT然后转换为十进制(无论如何,INT到十进制是隐式的)

select val, CAST((CONVERT(bigint, timestampcol)) as decimal) as 'TS as decimal' 
from teststmp

Answer 2

我认为这是一种更安全的方式。

SELECT CASE 
         WHEN Cast(timestampcol AS BIGINT) >= 0 THEN 
         Cast(timestampcol AS BIGINT) 
         ELSE 18446744073709551615 + Cast(timestampcol AS BIGINT)
       END 

下面显示了否则直接转换为 bigint 将返回负数，这可能不是所需的结果。

USE tempdb;

IF DB_ID('TestDBTS') IS NOT NULL
    DROP DATABASE TestDBTS;

CREATE DATABASE TestDBTS;


USE TestDBTS;

SELECT CAST(CAST(@@DBTS AS BIGINT) AS DECIMAL(20,0))
/*2000*/

/*Hack to manually set the timestamp. Undocumented, Unguaranteed & Dangerous!
  Do not use except on test databases.*/
DBCC WRITEPAGE(TestDBTS, 1, 9, 412, 8, 0xFFFFFFFFFFFFFF7F);


ALTER DATABASE TestDBTS SET OFFLINE WITH ROLLBACK IMMEDIATE;

ALTER DATABASE TestDBTS SET ONLINE WITH ROLLBACK IMMEDIATE;

USE TestDBTS;
SELECT CAST(CAST(@@DBTS AS BIGINT) AS DECIMAL(20,0))
/*9223372036854775807*/

CREATE TABLE T
(
X INT,
Y TIMESTAMP
)

INSERT INTO T(X) VALUES(1)

SELECT CAST(CAST(@@DBTS AS BIGINT) AS DECIMAL(20,0))
/*-9223372036854775807*/

SELECT CASE WHEN CAST(@@DBTS AS BIGINT) >= 0 
            THEN CAST(@@DBTS AS BIGINT)
            ELSE 18446744073709551615 + CAST(@@DBTS AS BIGINT) 
       END
/*9223372036854775808*/