Difference of two date time in sql server

Question

Is there any way to take the difference between two datetime in sql server?

For example, my dates are

1. 2010-01-22 15:29:55.090

Answer 1

There are a number of ways to look at a date difference, and more when comparing date/times. Here's what I use to get the difference between two dates formatted as "HH:MM:SS":

ElapsedTime AS
      RIGHT('0' + CAST(DATEDIFF(S, StartDate, EndDate)        / 3600 AS VARCHAR(2)), 2) + ':'
    + RIGHT('0' + CAST(DATEDIFF(S, StartDate, EndDate) % 3600 /   60 AS VARCHAR(2)), 2) + ':'
    + RIGHT('0' + CAST(DATEDIFF(S, StartDate, EndDate) %   60        AS VARCHAR(2)), 2)

I used this for a calculated column, but you could trivially rewrite it as a UDF or query calculation. Note that this logic rounds down fractional seconds; 00:00.00 to 00:00.999 is considered zero seconds, and displayed as "00:00:00".

If you anticipate that periods may be more than a few days long, this code switches to D:HH:MM:SS format when needed:

ElapsedTime AS
    CASE WHEN DATEDIFF(S, StartDate, EndDate) >= 359999
        THEN
                          CAST(DATEDIFF(S, StartDate, EndDate) / 86400        AS VARCHAR(7)) + ':'
            + RIGHT('0' + CAST(DATEDIFF(S, StartDate, EndDate) % 86400 / 3600 AS VARCHAR(2)), 2) + ':'
            + RIGHT('0' + CAST(DATEDIFF(S, StartDate, EndDate) %  3600 /   60 AS VARCHAR(2)), 2) + ':'
            + RIGHT('0' + CAST(DATEDIFF(S, StartDate, EndDate) %    60        AS VARCHAR(2)), 2)
        ELSE
              RIGHT('0' + CAST(DATEDIFF(S, StartDate, EndDate)        / 3600 AS VARCHAR(2)), 2) + ':'
            + RIGHT('0' + CAST(DATEDIFF(S, StartDate, EndDate) % 3600 /   60 AS VARCHAR(2)), 2) + ':'
            + RIGHT('0' + CAST(DATEDIFF(S, StartDate, EndDate) %   60        AS VARCHAR(2)), 2)
        END