How do I strip the date off of a datetime string i

问题:

I'm working on a data warehouse project and would like to know how to (preferably in a Derived Column component in a Data flow) strip the date piece off of a SQL datetime record.

Once I have the datetime converted to just a time I am going to do a lookup on the time to find the related time record in a time dimension table.

Can someone give me a simple function to accomplish this inside a derived column transform?

Example: Transform a datetime such as "12/02/2008 11:32:21 AM" into simply "11:32:21 AM".

回答1:

I would just do a cast to DT_DBTIME type (using Derived Column transform, or Convert type transform). DT_DBTIME contains just (hours, minutes, seconds) part of the date/time, so you'll get rid of the date part.

回答2:

If you need to do this in a variable expression Michael's solution won't work, but you can use the following expression:

(DT_DATE)(DT_DBDATE)GETDATE()

(DT_DBDATE) converts the current date and time to a date only. But the new datatype is not compatiple with SSIS's datetime. Therefore you'll have to use (DT_DATE) for converting to a compatible type.

Courtesy of this solution belongs to Russel Loski who has posted it in his blog: http://www.bidn.com/blogs/RussLoski/ssas/1458/converting-datetime-to-date-in-ssis

回答3:

Actually if you reverse the first 2 expressions like this: (DT_DBDATE)(DT_DATE)GETDATE() instead of (DT_DATE)(DT_DBDATE)GETDATE(), then you will TRUNCATE the time off the date field.

If the DT_DATE expression is before the DT_DBDATE expression, you will still have the time portion in your output, but it will be reset to all zeroes.

回答4:

Ran into this with writing a report for a scheduling app, needed the time that was stored as part of a datetime data type. I formated the datetime as 0 which gives you this mon dd yyyy hh:miAM (or PM), and just did a substring of that which returned the time only in an AM/PM format.

Example below.

DECLARE @S DATETIME = GETDATE()

SELECT SUBSTRING(CONVERT(NVARCHAR(30), @S , 0) , 13 , 10) AS ApptTime
    , CONVERT(NVARCHAR(30), @S , 0) AS ApptDate

回答5:

I personally use a series of functions for this. E.g.:

ALTER FUNCTION [dbo].[TIMEVALUE]
(
 @Datetime datetime
)
RETURNS datetime
AS
BEGIN
    RETURN (@Datetime - CAST(ROUND(CAST(@Datetime AS float), 0, 1) AS datetime))
END

I'd love to claim all the credit but it should really go to this guy.