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How to calculate age in T-SQL with years, months, and days
I'm simply trying to calc age (in years) using a birthdate variable
1932-04-29 00:00:00.000
and SYSDATETIME( ) in SQL Server, where by
SELECT year(Sysdatetime() - Birthdate) as Age
produces (surprisingly) : 1980
What did I miss? I expected to get 80!
Calculating age is not as simple as it might first appear.
If you use Datediff you get a difference in absolute years, which is not the age.
eg
select DATEDIFF(yy, '1980-12-31', getdate())
will return 32, whereas the age of the person in question is 31.
This might be accurate enough for your purposes.
More accurate, but still wrong, you can use
select convert(int,DATEDIFF(d, '1933-10-31', getdate())/365.25)
which is right most of the time.
Or you can write a more complex function....
CREATE Function [dbo].[F_GetAge]( #RefDate Datetime,#Birthdate Datetime) Returns Int as
/*
200040916 Thomas Wassermann
*/
Begin
Declare #Alter Int
if #RefDate>#Birthdate
Select #Alter=(DatePart(yy,CAst(#Refdate-#Birthdate -1 as Float))-1900)
else select #Alter=0
Return(#Alter)
end
Quick and dirty. Can have some errors bepending on leap years, etc.
-- quick and dirty age in years
declare #birthday datetime
set #birthday = '19320429'
-- this is pretty close, but could have problems with leap years, etc.
select floor(datediff(day, #birthday, CURRENT_TIMESTAMP) / 365.25)
What happens here is the following:
both dates get converted to floats as number of days since 1900-01-01T00:00:00
the floats get subtracted from each other yielding the number of days between them
the result gets converted back to a date by adding the number of days to the base date
To correctly calculate the difference use DATEDIFF: http://msdn.microsoft.com/en-us/library/ms189794.aspx
But there is still a problem with that. See here for a complete solution: How to calculate age (in years) based on Date of Birth and getDate()
Related
I'd like to figure out the age of a person based on two dates: their birthday and the date they were created in a database.
The age is being calculated in days instead of years, though. Here's my query:
SELECT date_of_birth as birthday, created_at, (created_at - date_of_birth) as Age
FROM public.users
WHERE date_of_birth IS NOT NULL
The date_of_birth field is a date w/o a timestamp, but the created_at field is a date with a timestamp (e.g. 2017-05-06 01:27:40).
And my output looks like this:
0 years 0 mons 9645 days 1 hours 27 mins 40.86485 secs
Any idea how can I round/calculate the ages by the nearest year?
Using PostgreSQL.
If you are using MS SQLServer than you could
CONVERT(DATE, created_at)
and than calculate difference in months like
DATEDIFF(month, created_at, GETDATE())/12
means you can use reminder in months to add or substract one year.
In PostgreSQL, dates are handled very differently to MSSQL & MySQL. In fact it follows the SQL standard very well, even if it’s not always intuitive.
To actually calculate the age of something, you can use age():
SELECT age(date1,date1)
Like all of PostgreSQL’s functions, there are variations of data type, and you may need to do something like this:
SELECT age(date1::date,date1::date)
or, more formally:
SELECT age(cast(date1 as date),cast(date1 as date))
The result will be an interval, which displays as a string :
SELECT age(current_date::date,'1981-01-17'::date);
-- 36 years 3 mons 22 days
If you just want the age in years, you can use extract:
SELECT extract('year' from age(current_date::date,'1981-01-17'::date));
Finally, if you want it correct to the nearest year, you can apply the old trick of adding half an interval:
extract('year' from age(current_date::date,'1981-01-17'::date)+interval '.5 year');
It’s not as simple as some of the other DBMS products, but it’s much more flexible, if you can get your head around it.
Here are some references:
https://www.postgresql.org/docs/current/static/functions-datetime.html
http://www.sqlines.com/postgresql/how-to/datediff
I am having trouble understanding this code. It actually seems to work, but I don't understand how the correct value for activity year and month is "found" get the proper min and max? Or is it running all permutations getting the highest? This is very strange to me.
I do understand how the dateadd works, just not how the query is actually working on the whole. This may be a bad question since I don't actually need help solving a problem, just insight into why this works.
select
EmployeeNumber,
sum(BaseCalculation) as BaseCalculation,
min(dateadd(mm, (ActivityYear - 1900) * 12 + ActivityMonth - 1 , 0)) as StartDate,
max(dateadd(mm, (ActivityYear - 1900) * 12 + ActivityMonth - 1 , 0)) as EndDate
from
Compensation
where
1=1
-- and
group by
EmployeeNumber
for both the min and max function call, the algorithm is
dateadd(mm, (ActivityYear - 1900) * 12 + ActivityMonth - 1 , 0)
Your query compute all possible date from the Compensation table using this algorithm. Then, you select the minimum date as StartDate and the maximum as EndDate.
This is how the proper max and min are returned.
Note that the dateadd signature is DATEADD (datepart , number , date )
Since the last parameter is 0, you are addind to month(mm) the number calculated in the algorithm, and return the corresponding date starting from 0.
Check this out for more information : https://msdn.microsoft.com/en-us/library/ms186819.aspx
It is converting the columns ActivityYear and ActivityMmonth to a date. It is doing so by counting the number of months since 1900 and adding them to time zero. So, Jan 2000 would become something like Jan, 100. This seems like a very arcane calculation, because dates that are about 2,000 years old are not really useful.
Of course, this assumes that ActivityYear is a recognizable recent year.
I would convert the year and month to the first day of the beginning of the month, with something like this:
min(cast(cast(ActivityYear * 10000 + ActivityMonth + 1 as varchar(255)) as date)
Sql Server will calculate every value of that statement, and then only return the min and max.
Although I cannot say for sure that sql server executes this way internally, the way I think about it I imagine that the engine strips off the group by and all the aggregate functions, runs that query. And then just sums/finds the min etc off of that.
I have two TIMESTAMP columns in my table: customer_birthday and purchase_date. I want to create a query to show the number of purchases by customer age, to create a chart.
But how do I calculate ages, in years, using BigQuery? In other words, how do I get the difference in years between two TIMESTAMPs? The age calculation cannot be made using days or hours, because of leap years, so the function DATEDIFF(<timestamp1>,<timestamp2>) is not appropriate.
Thanks.
First of all, I'd really love BigQuery to have a function which calculates current age based on a date. That seems to be like a very common use case and it's not really easy due to the whole leap year thing.
I found a great article about this issue: https://towardsdatascience.com/how-to-accurately-calculate-age-in-bigquery-999a8417e973
Their final approach is similar to Lars Haugseth's and Saad's answer, but they do not use the DAYOFYEAR part in order to avoid issues with leap years. It also gives you the flexibility not only to calculate the current age, but also the age at a particular date that you pass to the function as argument:
CREATE OR REPLACE FUNCTION workspace.age_calculation(as_of_date DATE, date_of_birth DATE)
AS (
DATE_DIFF(as_of_date,date_of_birth, YEAR) -
IF(EXTRACT(MONTH FROM date_of_birth)*100 + EXTRACT(DAY FROM date_of_birth) >
EXTRACT(MONTH FROM as_of_date)*100 + EXTRACT(DAY FROM as_of_date)
,1,0)
)
Regarding the difference between dates - you could consider user-defined functions (https://cloud.google.com/bigquery/user-defined-functions) with a JavaScript date library, such as Datejs or Moment.js
You can use DATE_DIFF to get the difference in years, but need to subtract by one if the birthday has not yet occured this year:
IF(EXTRACT(DAYOFYEAR FROM CURRENT_DATE) < EXTRACT(DAYOFYEAR FROM birthdate),
DATE_DIFF(CURRENT_DATE, birthdate, YEAR) - 1,
DATE_DIFF(CURRENT_DATE, birthdate, YEAR)) AS age
Here it is in a user defined function:
CREATE TEMP FUNCTION calculateAge(birthdate DATE) AS (
DATE_DIFF(CURRENT_DATE, birthdate, YEAR) +
IF(EXTRACT(DAYOFYEAR FROM CURRENT_DATE) < EXTRACT(DAYOFYEAR FROM birthdate), -1, 0) -- subtract 1 if bithdate has not yet occured this year
);
You can compute the number of days it would be if all years were 365 days long, take the difference, and divide by 365. For example:
SELECT (day2-day1)/365
FROM (
SELECT YEAR(t1) * 365 + DAYOFYEAR(t1) as day1,
YEAR(t2) * 365 + DAYOFYEAR(t2) as day2
FROM (
SELECT TIMESTAMP('20000201') as t1,
TIMESTAMP('20140201') as t2))
This returns 14.0, even though there are intervening leap years. If you want the final result as an integer instead of floating point, you can use the INTEGER() function to cast the result.
Note that if one of the dates is a leap day (feb 29) it will appear to be one year away from march 1, but I think this sounds like the intended behavior.
Another way to calculate age that takes leap years into account is to:
Calculate simple age based on difference in year
Either subtract 1 or not by:
Add difference in years to birthday (e.g. if today is 2022-12-14 and birthday is 2000-12-30, then the "new" birthday becomes 2022-12-30)
Do a DAY-based difference between today and "new" birthday, which either gives you a positive number (birthday passed for this year) or negative number (still has birthday this year)
Subtract 1 year from simple age calculation if number is negative
In BigQuery SQL code this looks like:
SELECT
bd AS birthday
,today
,DATE_DIFF(today, bd, YEAR) AS simpleAge
,DATE_DIFF(today, bd, YEAR) +
(CASE
WHEN DATE_DIFF(today, DATE_ADD(bd, INTERVAL DATE_DIFF(today, bd, YEAR) YEAR), DAY) >= 0
THEN 0
ELSE -1
END) AS age
FROM
(SELECT
PARSE_DATE("%Y-%m-%d", "2000-12-01") AS bd
,CURRENT_DATE("Asia/Tokyo") AS today
)
Outputs:
birthday
today
simpleAge
age
2000-12-30
2022-12-14
22
21
I found a place in our old code where the original programmer tried to calculate whether an employee had been hired for a certain number of years. The calculation used the difference in days between the date hired and today divided by 364. This didn't make sense to me so I changed it to the difference in years. This also seemed to give an incorrect answer. Does DateDiff round up to the nearest year? Running this formula in the immediate window gives 15 as the answer. I was hoping it would give 14.
?datediff("yyyy",#3/1/1999#,#2/19/2014#)
Would it be better to use.
?datediff("m",#3/1/1999#,#2/19/2014#)/12
DateDiff for years only considers the year parts of the dates you supply. And it does not return what you might want as "how many years" ...
For example, the last day of 2013 to the first day of 2014 would be one year as far as DateDiff("yyyy" is concerned.
? DateDiff("yyyy", #2013-12-31#, #2014-1-1#)
1
DateDiff rounds off to the very next year if the year difference is like x years and y months.
For example:
if a person's age is 18 years and 1 months, datediff(yy,DDOB,GetDate()) will give result as '19'.
In case you dont want this rounding off, you can
Get difference in days between two dates after casting them in
INTEGER
Divide the difference with 365.25
Use FLOOR to ignore the the decimal part (don't round off as the
next number):
FLOOR((CAST (GetDate() AS INTEGER) - CASR(YourDate AS INTEGER)) / 356.25)
You can do the combination of IIf,DateDiff and DateAdd, like this:
=IIf(DateDiff("m";DateAdd("yyyy";DateDiff("yyyy";[DDOB];Date());[DDOB]);Date())<0;
DateDiff("yyyy";[DDOB];Date())-1;
DateDiff("yyyy";[DDOB];Date()))
So, firstly you calculate months between DDOB plus DateDiff years and Date(), and if integer form DateDiff "m" are in minus, then IIf will reduce the value for the year for one.
I am trying to get the last of month, and in order to that i have written the following, to calculate the no. of days between today and the last date.
select datediff(DAY,GETDATE(),dateadd(m,1,getdate()))-GETDATE()
the bold part gives me the no. of days between today and a month from today, say 30 or 31. and then I am subtracting today's date from 30 or 31, which is " -getdate() "
The output for the above query is
1786-06-06 11:44:30.540
Could you please explain what is happening in the query? I am not looking for a solution, I would like to know how is SQL-Server interpreting the query.
Thanks. :)
The bold part of the expressions does not return a date, it returns a number of days:
31
Convert that to a datetime:
SELECT CONVERT(DATETIME, 31);
This is 31 days after day 0 (1900-01-01):
1900-02-01
Now, subtract GETDATE() as an integer (41512 days after day 0):
SELECT 31 - 41512 = -41481
Now add -41481 days to day 0:
SELECT DATEADD(DAY, -41481, 0);
-- or
SELECT DATEADD(DAY, -41481, '19000101');
Or:
SELECT CONVERT(DATETIME, 31 - CONVERT(INT, GETDATE()));
Now, I strongly recommend a couple of things:
Don't use implicit date math. #date_var_or_col - 1 for example fails with new data types like DATE and DATETIME2.
Don't use shorthand like m. If you mean MONTH, just take the massive productivity hit and type out MONTH. To see why, tell me if this provides the results you expect:
SELECT DATEPART(y, GETDATE()), DATEPART(w, GETDATE());
I am subtracting today's date from 30 or 31, which is " -getdate() "
Sounds like you understand exactly what is happening, but maybe don't understand the results.
You are implicitly converting GETDATE() to a number, which represents the number of days (and fractional days) since 1/1/1900 12:00:00 AM
When you "subtract" GETDATE() (41,511 as of 8/27/2013) from 30 or 31 you get an answer of -41,480, or 41,480 days before 1/1/1900, which would be about 6/6/1786 (plus or minus a few hours for the fractional part).