毫秒值未在SQL Server DateTime列中保存

Question

I need to store a DateTime value which is sent to the Database from a C# application which is using DateTime.UtcNow . If I save it to the DateTime column, the milliseconds value are always 000. But while debugging from the application, the milliseconds value is sent from the application to the database. What am I missing?

Answer 1

It might happen because datetime column rounds milliseconds part. From documentation;

Accuracy

Rounded to increments of .000 , .003 , or .007 seconds

Since you didn't show us how often you store your UtcNow value (I assume you store it as a DateTime , not it's string representation because parameterless ToString and other standard formats does not generates millisecond part usually ), this may happen but if you do it in short time intervals, it would be really weird always rounding to 000 as milliseconds part. But of course, we can't know that, yet.

On the other hand, datetime2 type does not do any rounding. And it's accuracy is 100 nanoseconds.

Accuracy

100 nanoseconds

Answer 2

Here's no pleasant way to use Datetime because

SQL Server only stores time to approximately 1/300th of a second. These always fall on the 0, 3 and 7 milliseconds

SQL Server 2008 has much more precision available. The datetime2 datatype will accurately store values like this: 2008-12-19 09:31:38.5670514

See reference documentation

Answer 3

It looks to me like something/someone is doing a default-ToString instead of using ToString with the proper ISO-standard format.

Proper ISO-format for date with time is

yyyy-MM-ddTHH:mm:ss.fff

while date-only ISO-format is

yyyyMMdd

You can check:

static void Main(string[] args)
{
    System.DateTime cur = System.DateTime.UtcNow;
    string strDefault = cur.ToString();
    string str  = cur.ToString("yyyy-MM-ddTHH:mm:ss.fff", System.Globalization.CultureInfo.InvariantCulture);
    System.Console.WriteLine(str);
    System.Console.WriteLine(strDefault);
}

This outputs

2016-03-03T08:31:27.324
03.03.2016 08:31:27

You might also want to use the HEX-format, as this enhances precision, or at least preserves a value that already was in SQL-Server. If you don't use hex-representation, you can get a 23:59:59.997 value from SQL-server and resave, and you'll have 00:00:00 with day+1. Using the hex-format preserves .997, while saving an ISO-string will yield day+1.

public static string GetTimeAsHex(System.DateTime dt)
{
    System.DateTime zero = new System.DateTime(1900, 1, 1);
    System.TimeSpan ts = dt - zero;
    System.TimeSpan ms = ts.Subtract(new System.TimeSpan(ts.Days, 0, 0, 0));

    double x = System.Math.Floor(ms.TotalMilliseconds / 3.3333333333);
    string hex = "0x" + ts.Days.ToString("X8") + System.Convert.ToInt32(x).ToString("X8");

    return hex;
}

Anyway, as others have already told you, SQL-server datetime is only precise to within a 4 ms error margin. This is why you should use datetime2, as it fixes many issues (bugs/"features") in datetime, including insufficient precision in the milliseconds range.

Answer 4

如果要将INSERT语句构建为string ，请尝试在字符串转换中指定毫秒输出

DateTime.UtcNow.ToString("yyyy-MM-dd HH:mm:ss.fff", CultureInfo.InvariantCulture);