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Doing subtraction on dates

Posted on 2004-08-20
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Last Modified: 2012-05-05
I need to determine the average age for a set of data. I have the create date for each record and need to subtract that to get the age of each row. Then I also need to sum that up so that I have the total and can get the average. Is there a way to do this using SQL?

Thanks,
John
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Question by:Pawlikj
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Dexstar earned 1000 total points
ID: 11854676
Pawlikj:

> I need to determine the average age for a set of data. I have the create date for
> each record and need to subtract that to get the age of each row. Then I also need
> to sum that up so that I have the total and can get the average. Is there a way to
> do this using SQL?

Yes, you can use the DATEDIFF function to get the age of the record.  Say you want to get the age in terms of "Days", you could do this:
    SELECT *, DATEDIFF(days, CreateDate, GETDATE()) As DaysOld FROM YourTable

However, if you just want to find the average, then SQL can do all the work for you:
    SELECT AVG( DATEDIFF(days, CreateDate, GETDATE()) ) As AverageDaysOld FROM YourTable

Hope That Helps,
Dex*
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Expert Comment

by:ram2098
ID: 11854679
You can use DATEDIFF function to find out the difference between two dates.

For syntax, check books online or

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts_da-db_5vxi.asp

Similarly, If you want to add the dates you can use DATADD function. But, not sure what is the requirement, looks like, for your query, it is a normal addition (not date additioin) to find the average.
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