Calculate time from begin date in SQL - sql

Question

I'm trying to tally up the number of unique ID accounts that are active for more than a year as well as include how long each one is active. The problem with the code I have is it's not including accounts that are currently active (ones that don't have an end date). For example, if the begin date was May 01 2018 but has no end date since it's currently active, it should also be included in this query. Here's what I have so far..
SELECT UniqueID,
DATEDIFF(yy, Begin_Date,End_Date) as timeactive
FROM TABLE
WHERE DATEDIFF(yy, Begin_Date,End_Date) > 1
I want my output to look like...
Unique ID Time active
F000012 2.5
F000031 1.5
This is what ended up working:
SELECT UniqueID,
CAST(ROUND(DATEDIFF(day, Begin_Date, COALESCE(End_Date, getdate()))/365.0, 1, 0) AS NUMERIC (10,1)) as timeactive
FROM TABLE
WHERE DATEDIFF(day, Begin_Date, COALESCE (End_Date, getdate())) >= 365

Answer 1

If the EndDate is null then the output of the DateDiff function will be null, and any null compared to anything (even another null) is a result of null (usually then interpreted as false)
I suggest you use COALESCE to convert your end date to today if it is null:
SELECT
UniqueID,
DATEDIFF(yy, Begin_Date,COALESCE(End_Date, GetUtcDate()) as timeactive
FROM TABLE
WHERE DATEDIFF(yy, Begin_Date,COALESCE(End_Date, GetUtcDate()) > 1
You should bear in mind that the DATEDIFF function as used here, in SQLserver does NOT return the amount of time that has passed between the two dates. It returns the number of times the named interval has changed between the two dates
For example, DATEDIFF(year, 2000-01-01, 2000-12-31 23:59:59) will return 0 because these are both year 2000 even though they're just one second short of being a year apart. If you do DATEDIFF(year, 2000-12-31 23:59:59, 2001-01-01 00:00:01) even though these dates are only two seconds apart datediff will report them as 1 year apart because the year number has changed from 2000 to 2001.
DATEDIFF counts up by one every time the clock rolls past an interval change and in this case the interval is Year
To get your dates to report as 1.5 years etc you should consider to datediff by a smaller interval and divide, such as asking for the DAYS diff between two dates and then dividing by 365.25- the average number of days in a year. The smaller the interval you ask datediff for the more accurate the result will be but it'll never be 100%. If you're only after results to one decimal place of a year then days will be accurate enough
To get 1 decimal place, cast to a numeric with 1 DP:
SELECT
UniqueID,
CAST(DATEDIFF(day, Begin_Date,COALESCE(End_Date, GetUtcDate())/365.25 AS NUMERIC(5,1)) as timeactive
FROM TABLE
WHERE DATEDIFF(day, Begin_Date,COALESCE(End_Date, GetUtcDate()) >= 365

Answer 2

If you want time active as fractional years, then you need to use a smaller unit of time and divide. For instance:
SELECT UniqueID,
DATEDIFF(month, Begin_Date, COALESCE(End_Date, GETDATE())) / 12.0 as timeactive
FROM TABLE
WHERE Begin_Date < DATEADD(YEAR, -1, COALESCE(End_Date, GETDATE()))
Note the change in the WHERE clause. DATEDIFF() counts the number of year boundaries between dates. So the difference in years between 2019-01-01 and 2020-12-31 is the same as the difference between 2019-12-31 and 2020-01-01 -- exactly 1.

Answer 3

Consider:
SELECT
UniqueID,
DATEDIFF(yy, Begin_Date, COALESCE(End_Date, getdate()) as timeactive
FROM TABLE
WHERE DATEDIFF(yy, Begin_Date, COALESCE(End_Date, getdate()) > 1
This works by using the current date as default value for empty End_Dates. So this allows records with empty end date if their start date is more than one year ago.