T-SQL Count days between two days (datediff not quite working) - sql-server

We have a requirement to bill our customers per day. We bill for an asset's existence in our system on that day. So, I started with datediff...
select datediff(dd ,'2015-04-24 12:59:32.050' ,'2015-05-01 00:59:59.000');
Returns this:
7
But I need to count the following dates: 4/24,4/25,4/26,4/27,4/28,4/29, 4/30, 5/1, which are 8 days. So datediff isn't quite working right. I tried these variations below
--too simple, returns 7, i need it to return 8
select datediff(dd ,'2015-04-24 12:59:32.050', '2015-05-01 23:59:59.000');
--looking better, this returns the 8 i need
select ceiling(datediff(hh,'2015-04-24 12:59:32.050', '2015-05-01 23:59:59.000')/24.0);
-- returns 7, even though the answer still needs to be 8. (changed enddate)
select ceiling(datediff(hh,'2015-04-24 12:59:32.050', '2015-05-01 00:59:59.000')/24.0);
So, my question... How, in SQL, would I derive the date count like i described, since I believe datediff counts the number of day boundaries crossed.... My current best approach is loop through each day in a cursor and count. Ick.


Use CONVERT to get rid of the time part, add 1 to get the desired result:
SELECT DATEDIFF(dd,
CONVERT(DATE, '2015-04-24 12:59:32.050'),
CONVERT(DATE, '2015-05-01 00:59:59.000')) + 1;
It turns out the time part does not play any significant role in DATEDIFF when dd is used as the datepart argument. Hence, CONVERT is redundant. This:
SELECT DATEDIFF(dd, '2015-04-24 23:59:59.59','2015-05-01 00:00:00.000') + 1
will return 8 as well.


You could try this which would return 8 days.
select datediff(dd ,'2015-04-24 12:59:32.050' ,CASE DATEDIFF(Second,'2015-05-01 00:00:00.000','2015-05-01 23:59:59.000') WHEN 0 THEN '2015-05-01 23:59:59.000' ELSE DATEADD(dd,+1,'2015-05-01 23:59:59.000') END)
If you want to use variables for your dates then something like this would work.
BEGIN
DECLARE #StartDate DATETIME
DECLARE #EndDate DATETIME
DECLARE #EndDateOnly DATE
SET #StartDate = '2015-04-24 12:59:32.050'
SET #EndDate = '2015-05-01 23:59:59.000'
SET #EndDateOnly = CAST(#EndDate AS DATE)
SELECT datediff(dd ,#StartDate ,CASE DATEDIFF(Second,CAST(#EndDateOnly||' 00:00:00.000' AS DATETIME),#EndDate) WHEN 0 THEN #EndDate ELSE DATEADD(dd,+1,#EndDate) END)
END

Related

Evaluating datetime into timewindows

Im trying to establish for any given datetime a tag that is purely dependent on the time part.
However because the time part is cyclic I cant make it work with simple greater lower than conditions.
I tried a lot of casting and shift one time to 24hour mark to kinda break the cycle However it just gets more and more complicated and still doesnt work.
Im using SQL-Server, here is the situation:
DECLARE #tagtable TABLE (tag varchar(10),[start] time,[end] time);
DECLARE #datetimestable TABLE ([timestamp] datetime)
Insert Into #tagtable (tag, [start], [end])
values ('tag1','04:00:00.0000000','11:59:59.9999999'),
('tag2','12:00:00.0000000','19:59:59.9999999'),
('tag3','20:00:00.0000000','03:59:59.9999999');
Insert Into #datetimestable ([timestamp])
values ('2022-07-24T23:05:23.120'),
('2022-07-27T13:24:40.650'),
('2022-07-26T09:00:00.000');
tagtable:
tag
start
end
tag1
04:00:00.0000000
11:59:59.9999999
tag2
12:00:00.0000000
19:59:59.9999999
tag3
20:00:00.0000000
03:59:59.9999999
for given datetimes e.g. 2022-07-24 23:05:23.120, 2022-07-27 13:24:40.650, 2022-07-26 09:00:00.000
the desired result would be:
date
tag
2022-07-25
tag3
2022-07-27
tag2
2022-07-26
tag1
As I wrote i tried to twist this with casts and adding and datediffs
SELECT
If(Datepart(Hour, a.[datetime]) > 19,
Cast(Dateadd(Day,1,a.[datetime]) as Date),
Cast(a.[datetime] as Date)
) as [date],
b.[tag]
FROM #datetimestable a
INNER JOIN #tagtable b
ON SomethingWith(a.[datetime])
between SomethingWith(b.[start]) and SomethingWith(b.[end])

The only tricky bit here is that your tag time ranges can go over midnight, so you need to check that your time is either between start and end, or if it spans midnight its between start and 23:59:59 or between 00:00:00 and end.
The only other piece is splitting your timestamp column into date and time using a CTE, to save having to repeat the cast.
;WITH splitTimes AS
(
SELECT CAST(timestamp AS DATE) as D,
CAST(timestamp AS TIME) AS T
FROM #datetimestable
)
SELECT
DATEADD(
day,
CASE WHEN b.[end]<b.start THEN 1 ELSE 0 END,
a.D) as timestamp,
b.[tag]
FROM [splitTimes] a
INNER JOIN #tagtable b
ON a.T between b.[start] and b.[end]
OR (b.[end]<b.start AND (a.T BETWEEN b.[start] AND '23:59:59.99999'
OR a.T BETWEEN '00:00:00' AND b.[end]))
Live example: https://dbfiddle.uk/?rdbms=sqlserver_2019&fiddle=506aef05b5a761afaf1f67a6d729446c

Since they're all 8-hour shifts, we can essentially ignore the end (though, generally, trying to say an end time is some specific precision of milliseconds will lead to a bad time if you ever use a different data type (see the first section here) - so if the shift length will change, just put the beginning of the next shift and use >= start AND < end instead of BETWEEN).
;WITH d AS
(
SELECT datetime = [timestamp],
date = CONVERT(datetime, CONVERT(date, [timestamp]))
FROM dbo.datetimestable
)
SELECT date = DATEADD(DAY,
CASE WHEN t.start > t.[end] THEN 1 ELSE 0 END,
CONVERT(date, date)),
t.tag
FROM d
INNER JOIN dbo.tagtable AS t
ON d.datetime >= DATEADD(HOUR, DATEPART(HOUR, t.start), d.date)
AND d.datetime < DATEADD(HOUR, 8, DATEADD(HOUR,
DATEPART(HOUR, t.start), d.date));
Example db<>fiddle

Here's a completely different approach that defines the intervals in terms of starts and durations rather than starts and ends.
This allows the creation of tags that can span multiple days, which might seem like an odd capability to have here, but there might be a use for it if we add some more conditions down the line. For example, say we want to be able say "anything from 6pm friday to 9am monday gets the 'out of hours' tag". Then we could add a day of week predicate to the tag definition, and still use the duration-based interval.
I have defined the duration granularity in terms of hours, but of course this can easily be changed
create table #tags
(
tag varchar(10),
startTimeInclusive time,
durationHours int
);
insert #tags
values ('tag1','04:00:00', 8),
('tag2','12:00:00', 8),
('tag3','20:00:00', 8);
create table #dateTimes (dt datetime)
insert #dateTimes
values ('2022-07-24T23:05:23.120'),
('2022-07-27T13:24:40.650'),
('2022-07-26T09:00:00.000');
select dt.dt,
t.tag
from #datetimes dt
join #tags t on cast(dt.dt as time) >= t.startTimeInclusive
and dt.dt < dateadd
(
hour,
t.durationHours,
cast(cast(dt.dt as date) as datetime) -- strip the time from dt
+ cast(t.startTimeInclusive as datetime) -- add back the time from t
);

Maybe I am looking at this to simple, but,
can't you just take the first tag with an hour greater then your hour in table datetimestable.
With an order by desc it should always give you the correct tag.
This will work well as long as you have no gaps in your tagtable
select case when datepart(hour, tag.tagStart) > 19 then dateadd(day, 1, convert(date, dt.timestamp))
else convert(date, dt.timestamp)
end as [date],
tag.tag
from datetimestable dt
outer apply ( select top 1
tt.tag,
tt.tagStart
from tagtable tt
where datepart(Hour, dt.timestamp) > datepart(hour, tt.tagStart)
order by tt.tagStart desc
) tag
It returns the correct result in this DBFiddle
The result is
date
tag
2022-07-25
tag3
2022-07-27
tag2
2022-07-26
tag1
EDIT
If it is possible that there are gaps in the table,
then I think the most easy and solid solution would be to split that row that passes midnight into 2 rows, and then your query can be very simple
See this DBFiddle
select case when datepart(hour, tag.tagStart) > 19 then dateadd(day, 1, convert(date, dt.timestamp))
else convert(date, dt.timestamp)
end as [date],
tag.tag
from datetimestable dt
outer apply ( select tt.tag,
tt.tagStart
from tagtable tt
where datepart(Hour, dt.timestamp) >= datepart(hour, tt.tagStart)
and datepart(Hour, dt.timestamp) <= datepart(hour, tt.tagEnd)
) tag

Find age between 15 to 25 years from a given column of date of birth? [duplicate]

I have a table listing people along with their date of birth (currently a nvarchar(25))
How can I convert that to a date, and then calculate their age in years?
My data looks as follows
ID Name DOB
1 John 1992-01-09 00:00:00
2 Sally 1959-05-20 00:00:00
I would like to see:
ID Name AGE DOB
1 John 17 1992-01-09 00:00:00
2 Sally 50 1959-05-20 00:00:00

There are issues with leap year/days and the following method, see the update below:
try this:
DECLARE #dob datetime
SET #dob='1992-01-09 00:00:00'
SELECT DATEDIFF(hour,#dob,GETDATE())/8766.0 AS AgeYearsDecimal
,CONVERT(int,ROUND(DATEDIFF(hour,#dob,GETDATE())/8766.0,0)) AS AgeYearsIntRound
,DATEDIFF(hour,#dob,GETDATE())/8766 AS AgeYearsIntTrunc
OUTPUT:
AgeYearsDecimal AgeYearsIntRound AgeYearsIntTrunc
--------------------------------------- ---------------- ----------------
17.767054 18 17
(1 row(s) affected)
UPDATE here are some more accurate methods:
BEST METHOD FOR YEARS IN INT
DECLARE #Now datetime, #Dob datetime
SELECT #Now='1990-05-05', #Dob='1980-05-05' --results in 10
--SELECT #Now='1990-05-04', #Dob='1980-05-05' --results in 9
--SELECT #Now='1989-05-06', #Dob='1980-05-05' --results in 9
--SELECT #Now='1990-05-06', #Dob='1980-05-05' --results in 10
--SELECT #Now='1990-12-06', #Dob='1980-05-05' --results in 10
--SELECT #Now='1991-05-04', #Dob='1980-05-05' --results in 10
SELECT
(CONVERT(int,CONVERT(char(8),#Now,112))-CONVERT(char(8),#Dob,112))/10000 AS AgeIntYears
you can change the above 10000 to 10000.0 and get decimals, but it will not be as accurate as the method below.
BEST METHOD FOR YEARS IN DECIMAL
DECLARE #Now datetime, #Dob datetime
SELECT #Now='1990-05-05', #Dob='1980-05-05' --results in 10.000000000000
--SELECT #Now='1990-05-04', #Dob='1980-05-05' --results in 9.997260273973
--SELECT #Now='1989-05-06', #Dob='1980-05-05' --results in 9.002739726027
--SELECT #Now='1990-05-06', #Dob='1980-05-05' --results in 10.002739726027
--SELECT #Now='1990-12-06', #Dob='1980-05-05' --results in 10.589041095890
--SELECT #Now='1991-05-04', #Dob='1980-05-05' --results in 10.997260273973
SELECT 1.0* DateDiff(yy,#Dob,#Now)
+CASE
WHEN #Now >= DATEFROMPARTS(DATEPART(yyyy,#Now),DATEPART(m,#Dob),DATEPART(d,#Dob)) THEN --birthday has happened for the #now year, so add some portion onto the year difference
( 1.0 --force automatic conversions from int to decimal
* DATEDIFF(day,DATEFROMPARTS(DATEPART(yyyy,#Now),DATEPART(m,#Dob),DATEPART(d,#Dob)),#Now) --number of days difference between the #Now year birthday and the #Now day
/ DATEDIFF(day,DATEFROMPARTS(DATEPART(yyyy,#Now),1,1),DATEFROMPARTS(DATEPART(yyyy,#Now)+1,1,1)) --number of days in the #Now year
)
ELSE --birthday has not been reached for the last year, so remove some portion of the year difference
-1 --remove this fractional difference onto the age
* ( -1.0 --force automatic conversions from int to decimal
* DATEDIFF(day,DATEFROMPARTS(DATEPART(yyyy,#Now),DATEPART(m,#Dob),DATEPART(d,#Dob)),#Now) --number of days difference between the #Now year birthday and the #Now day
/ DATEDIFF(day,DATEFROMPARTS(DATEPART(yyyy,#Now),1,1),DATEFROMPARTS(DATEPART(yyyy,#Now)+1,1,1)) --number of days in the #Now year
)
END AS AgeYearsDecimal

Gotta throw this one out there. If you convert the date using the 112 style (yyyymmdd) to a number you can use a calculation like this...
(yyyyMMdd - yyyyMMdd) / 10000 = difference in full years
declare #as_of datetime, #bday datetime;
select #as_of = '2009/10/15', #bday = '1980/4/20'
select
Convert(Char(8),#as_of,112),
Convert(Char(8),#bday,112),
0 + Convert(Char(8),#as_of,112) - Convert(Char(8),#bday,112),
(0 + Convert(Char(8),#as_of,112) - Convert(Char(8),#bday,112)) / 10000
output
20091015 19800420 290595 29

I have used this query in our production code for nearly 10 years:
SELECT FLOOR((CAST (GetDate() AS INTEGER) - CAST(Date_of_birth AS INTEGER)) / 365.25) AS Age

You need to consider the way the datediff command rounds.
SELECT CASE WHEN dateadd(year, datediff (year, DOB, getdate()), DOB) > getdate()
THEN datediff(year, DOB, getdate()) - 1
ELSE datediff(year, DOB, getdate())
END as Age
FROM <table>
Which I adapted from here.
Note that it will consider 28th February as the birthday of a leapling for non-leap years e.g. a person born on 29 Feb 2020 will be considered 1 year old on 28 Feb 2021 instead of 01 Mar 2021.

So many of the above solutions are wrong DateDiff(yy,#Dob, #PassedDate) will not consider the month and day of both dates. Also taking the dart parts and comparing only works if they're properly ordered.
THE FOLLOWING CODE WORKS AND IS VERY SIMPLE:
create function [dbo].[AgeAtDate](
#DOB datetime,
#PassedDate datetime
)
returns int
with SCHEMABINDING
as
begin
declare #iMonthDayDob int
declare #iMonthDayPassedDate int
select #iMonthDayDob = CAST(datepart (mm,#DOB) * 100 + datepart (dd,#DOB) AS int)
select #iMonthDayPassedDate = CAST(datepart (mm,#PassedDate) * 100 + datepart (dd,#PassedDate) AS int)
return DateDiff(yy,#DOB, #PassedDate)
- CASE WHEN #iMonthDayDob <= #iMonthDayPassedDate
THEN 0
ELSE 1
END
End

EDIT: THIS ANSWER IS INCORRECT. I leave it in here as a warning to anyone tempted to use dayofyear, with a further edit at the end.
If, like me, you do not want to divide by fractional days or risk rounding/leap year errors, I applaud #Bacon Bits comment in a post above https://stackoverflow.com/a/1572257/489865 where he says:
If we're talking about human ages, you should calculate it the way
humans calculate age. It has nothing to do with how fast the earth
moves and everything to do with the calendar. Every time the same
month and day elapses as the date of birth, you increment age by 1.
This means the following is the most accurate because it mirrors what
humans mean when they say "age".
He then offers:
DATEDIFF(yy, #date, GETDATE()) -
CASE WHEN (MONTH(#date) > MONTH(GETDATE())) OR (MONTH(#date) = MONTH(GETDATE()) AND DAY(#date) > DAY(GETDATE()))
THEN 1 ELSE 0 END
There are several suggestions here involving comparing the month & day (and some get it wrong, failing to allow for the OR as correctly here!). But nobody has offered dayofyear, which seems so simple and much shorter. I offer:
DATEDIFF(year, #date, GETDATE()) -
CASE WHEN DATEPART(dayofyear, #date) > DATEPART(dayofyear, GETDATE()) THEN 1 ELSE 0 END
[Note: Nowhere in SQL BOL/MSDN is what DATEPART(dayofyear, ...) returns actually documented! I understand it to be a number in the range 1--366; most importantly, it does not change by locale as per DATEPART(weekday, ...) & SET DATEFIRST.]
EDIT: Why dayofyear goes wrong: As user #AeroX has commented, if the birth/start date is after February in a non leap year, the age is incremented one day early when the current/end date is a leap year, e.g. '2015-05-26', '2016-05-25' gives an age of 1 when it should still be 0. Comparing the dayofyear in different years is clearly dangerous. So using MONTH() and DAY() is necessary after all.

I believe this is similar to other ones posted here.... but this solution worked for the leap year examples 02/29/1976 to 03/01/2011 and also worked for the case for the first year.. like 07/04/2011 to 07/03/2012 which the last one posted about leap year solution did not work for that first year use case.
SELECT FLOOR(DATEDIFF(DAY, #date1 , #date2) / 365.25)
Found here.

Since there isn't one simple answer that always gives the correct age, here's what I came up with.
SELECT DATEDIFF(YY, DateOfBirth, GETDATE()) -
CASE WHEN RIGHT(CONVERT(VARCHAR(6), GETDATE(), 12), 4) >=
RIGHT(CONVERT(VARCHAR(6), DateOfBirth, 12), 4)
THEN 0 ELSE 1 END AS AGE
This gets the year difference between the birth date and the current date. Then it subtracts a year if the birthdate hasn't passed yet.
Accurate all the time - regardless of leap years or how close to the birthdate.
Best of all - no function.

I've done a lot of thinking and searching about this and I have 3 solutions that
calculate age correctly
are short (mostly)
are (mostly) very understandable.
Here are testing values:
DECLARE #NOW DATETIME = '2013-07-04 23:59:59'
DECLARE #DOB DATETIME = '1986-07-05'
Solution 1: I found this approach in one js library. It's my favourite.
DATEDIFF(YY, #DOB, #NOW) -
CASE WHEN DATEADD(YY, DATEDIFF(YY, #DOB, #NOW), #DOB) > #NOW THEN 1 ELSE 0 END
It's actually adding difference in years to DOB and if it is bigger than current date then subtracts one year. Simple right? The only thing is that difference in years is duplicated here.
But if you don't need to use it inline you can write it like this:
DECLARE #AGE INT = DATEDIFF(YY, #DOB, #NOW)
IF DATEADD(YY, #AGE, #DOB) > #NOW
SET #AGE = #AGE - 1
Solution 2: This one I originally copied from #bacon-bits. It's the easiest to understand but a bit long.
DATEDIFF(YY, #DOB, #NOW) -
CASE WHEN MONTH(#DOB) > MONTH(#NOW)
OR MONTH(#DOB) = MONTH(#NOW) AND DAY(#DOB) > DAY(#NOW)
THEN 1 ELSE 0 END
It's basically calculating age as we humans do.
Solution 3: My friend refactored it into this:
DATEDIFF(YY, #DOB, #NOW) -
CEILING(0.5 * SIGN((MONTH(#DOB) - MONTH(#NOW)) * 50 + DAY(#DOB) - DAY(#NOW)))
This one is the shortest but it's most difficult to understand. 50 is just a weight so the day difference is only important when months are the same. SIGN function is for transforming whatever value it gets to -1, 0 or 1. CEILING(0.5 * is the same as Math.max(0, value) but there is no such thing in SQL.

What about:
DECLARE #DOB datetime
SET #DOB='19851125'
SELECT Datepart(yy,convert(date,GETDATE())-#DOB)-1900
Wouldn't that avoid all those rounding, truncating and ofsetting issues?

Just check whether the below answer is feasible.
DECLARE #BirthDate DATE = '09/06/1979'
SELECT
(
YEAR(GETDATE()) - YEAR(#BirthDate) -
CASE WHEN (MONTH(GETDATE()) * 100) + DATEPART(dd, GETDATE()) >
(MONTH(#BirthDate) * 100) + DATEPART(dd, #BirthDate)
THEN 1
ELSE 0
END
)

select floor((datediff(day,0,#today) - datediff(day,0,#birthdate)) / 365.2425) as age
There are a lot of 365.25 answers here. Remember how leap years are defined:
Every four years
except every 100 years
except every 400 years

There are many answers to this question, but I think this one is close to the truth.
The datediff(year,…,…) function, as we all know, only counts the boundaries crossed by the date part, in this case the year. As a result it ignores the rest of the year.
This will only give the age in completed years if the year were to start on the birthday. It probably doesn’t, but we can fake it by adjusting the asking date back by the same amount.
In pseudopseudo code, it’s something like this:
adjusted_today = today - month(dob) + 1 - day(dob) + 1
age = year(adjusted_today - dob)
The + 1 is to allow for the fact that the month and day numbers start from 1 and not 0.
The reason we subtract the month and the day separately rather than the day of the year is because February has the annoying tendency to change its length.
The calculation in SQL is:
datediff(year,dob,dateadd(month,-month(dob)+1,dateadd(day,-day(dob)+1,today)))
where dob and today are presumed to be the date of birth and the asking date.
You can test this as follows:
WITH dates AS (
SELECT
cast('2022-03-01' as date) AS today,
cast('1943-02-25' as date) AS dob
)
select
datediff(year,dob,dateadd(month,-month(dob)+1,dateadd(day,-day(dob)+1,today))) AS age
from dates;
which gives you George Harrison’s age in completed years.
This is much cleaner than fiddling about with quarter days which will generally give you misleading values on the edges.
If you have the luxury of creating a scalar function, you can use something like this:
DROP FUNCTION IF EXISTS age;
GO
CREATE FUNCTION age(#dob date, #today date) RETURNS INT AS
BEGIN
SET #today = dateadd(month,-month(#dob)+1,#today);
SET #today = dateadd(day,-day(#dob)+1,#today);
RETURN datediff(year,#dob,#today);
END;
GO
Remember, you need to call dbo.age() because, well, Microsoft.

DECLARE #DOB datetime
set #DOB ='11/25/1985'
select floor(
( cast(convert(varchar(8),getdate(),112) as int)-
cast(convert(varchar(8),#DOB,112) as int) ) / 10000
)
source: http://beginsql.wordpress.com/2012/04/26/how-to-calculate-age-in-sql-server/

Try This
DECLARE #date datetime, #tmpdate datetime, #years int, #months int, #days int
SELECT #date = '08/16/84'
SELECT #tmpdate = #date
SELECT #years = DATEDIFF(yy, #tmpdate, GETDATE()) - CASE WHEN (MONTH(#date) > MONTH(GETDATE())) OR (MONTH(#date) = MONTH(GETDATE()) AND DAY(#date) > DAY(GETDATE())) THEN 1 ELSE 0 END
SELECT #tmpdate = DATEADD(yy, #years, #tmpdate)
SELECT #months = DATEDIFF(m, #tmpdate, GETDATE()) - CASE WHEN DAY(#date) > DAY(GETDATE()) THEN 1 ELSE 0 END
SELECT #tmpdate = DATEADD(m, #months, #tmpdate)
SELECT #days = DATEDIFF(d, #tmpdate, GETDATE())
SELECT Convert(Varchar(Max),#years)+' Years '+ Convert(Varchar(max),#months) + ' Months '+Convert(Varchar(Max), #days)+'days'

After trying MANY methods, this works 100% of the time using the modern MS SQL FORMAT function instead of convert to style 112. Either would work but this is the least code.
Can anyone find a date combination which does not work? I don't think there is one :)
--Set parameters, or choose from table.column instead:
DECLARE #DOB DATE = '2000/02/29' -- If #DOB is a leap day...
,#ToDate DATE = '2018/03/01' --...there birthday in this calculation will be
--0+ part tells SQL to calc the char(8) as numbers:
SELECT [Age] = (0+ FORMAT(#ToDate,'yyyyMMdd') - FORMAT(#DOB,'yyyyMMdd') ) /10000

CASE WHEN datepart(MM, getdate()) < datepart(MM, BIRTHDATE) THEN ((datepart(YYYY, getdate()) - datepart(YYYY, BIRTH_DATE)) -1 )
ELSE
CASE WHEN datepart(MM, getdate()) = datepart(MM, BIRTHDATE)
THEN
CASE WHEN datepart(DD, getdate()) < datepart(DD, BIRTHDATE) THEN ((datepart(YYYY, getdate()) - datepart(YYYY, BIRTHDATE)) -1 )
ELSE (datepart(YYYY, getdate()) - datepart(YYYY, BIRTHDATE))
END
ELSE (datepart(YYYY, getdate()) - datepart(YYYY, BIRTHDATE)) END
END

SELECT ID,
Name,
DATEDIFF(yy,CONVERT(DATETIME, DOB),GETDATE()) AS AGE,
DOB
FROM MyTable

How about this:
SET #Age = CAST(DATEDIFF(Year, #DOB, #Stamp) as int)
IF (CAST(DATEDIFF(DAY, DATEADD(Year, #Age, #DOB), #Stamp) as int) < 0)
SET #Age = #Age - 1

Try this solution:
declare #BirthDate datetime
declare #ToDate datetime
set #BirthDate = '1/3/1990'
set #ToDate = '1/2/2008'
select #BirthDate [Date of Birth], #ToDate [ToDate],(case when (DatePart(mm,#ToDate) < Datepart(mm,#BirthDate))
OR (DatePart(m,#ToDate) = Datepart(m,#BirthDate) AND DatePart(dd,#ToDate) < Datepart(dd,#BirthDate))
then (Datepart(yy, #ToDate) - Datepart(yy, #BirthDate) - 1)
else (Datepart(yy, #ToDate) - Datepart(yy, #BirthDate))end) Age

This will correctly handle the issues with the birthday and rounding:
DECLARE #dob datetime
SET #dob='1992-01-09 00:00:00'
SELECT DATEDIFF(YEAR, '0:0', getdate()-#dob)

Ed Harper's solution is the simplest I have found which never returns the wrong answer when the month and day of the two dates are 1 or less days apart. I made a slight modification to handle negative ages.
DECLARE #D1 AS DATETIME, #D2 AS DATETIME
SET #D2 = '2012-03-01 10:00:02'
SET #D1 = '2013-03-01 10:00:01'
SELECT
DATEDIFF(YEAR, #D1,#D2)
+
CASE
WHEN #D1<#D2 AND DATEADD(YEAR, DATEDIFF(YEAR,#D1, #D2), #D1) > #D2
THEN - 1
WHEN #D1>#D2 AND DATEADD(YEAR, DATEDIFF(YEAR,#D1, #D2), #D1) < #D2
THEN 1
ELSE 0
END AS AGE

The answer marked as correct is nearer to accuracy but, it fails in following scenario - where Year of birth is Leap year and day are after February month
declare #ReportStartDate datetime = CONVERT(datetime, '1/1/2014'),
#DateofBirth datetime = CONVERT(datetime, '2/29/1948')
FLOOR(DATEDIFF(HOUR,#DateofBirth,#ReportStartDate )/8766)
OR
FLOOR(DATEDIFF(HOUR,#DateofBirth,#ReportStartDate )/8765.82) -- Divisor is more accurate than 8766
-- Following solution is giving me more accurate results.
FLOOR(DATEDIFF(YEAR,#DateofBirth,#ReportStartDate) - (CASE WHEN DATEADD(YY,DATEDIFF(YEAR,#DateofBirth,#ReportStartDate),#DateofBirth) > #ReportStartDate THEN 1 ELSE 0 END ))
It worked in almost all scenarios, considering leap year, date as 29 feb, etc.
Please correct me if this formula have any loophole.

Declare #dob datetime
Declare #today datetime
Set #dob = '05/20/2000'
set #today = getdate()
select CASE
WHEN dateadd(year, datediff (year, #dob, #today), #dob) > #today
THEN datediff (year, #dob, #today) - 1
ELSE datediff (year, #dob, #today)
END as Age

Here is how i calculate age given a birth date and current date.
select case
when cast(getdate() as date) = cast(dateadd(year, (datediff(year, '1996-09-09', getdate())), '1996-09-09') as date)
then dateDiff(yyyy,'1996-09-09',dateadd(year, 0, getdate()))
else dateDiff(yyyy,'1996-09-09',dateadd(year, -1, getdate()))
end as MemberAge
go

CREATE function dbo.AgeAtDate(
#DOB datetime,
#CompareDate datetime
)
returns INT
as
begin
return CASE WHEN #DOB is null
THEN
null
ELSE
DateDiff(yy,#DOB, #CompareDate)
- CASE WHEN datepart(mm,#CompareDate) > datepart(mm,#DOB) OR (datepart(mm,#CompareDate) = datepart(mm,#DOB) AND datepart(dd,#CompareDate) >= datepart(dd,#DOB))
THEN 0
ELSE 1
END
END
End
GO

DECLARE #FromDate DATETIME = '1992-01-2623:59:59.000',
#ToDate DATETIME = '2016-08-10 00:00:00.000',
#Years INT, #Months INT, #Days INT, #tmpFromDate DATETIME
SET #Years = DATEDIFF(YEAR, #FromDate, #ToDate)
- (CASE WHEN DATEADD(YEAR, DATEDIFF(YEAR, #FromDate, #ToDate),
#FromDate) > #ToDate THEN 1 ELSE 0 END)
SET #tmpFromDate = DATEADD(YEAR, #Years , #FromDate)
SET #Months = DATEDIFF(MONTH, #tmpFromDate, #ToDate)
- (CASE WHEN DATEADD(MONTH,DATEDIFF(MONTH, #tmpFromDate, #ToDate),
#tmpFromDate) > #ToDate THEN 1 ELSE 0 END)
SET #tmpFromDate = DATEADD(MONTH, #Months , #tmpFromDate)
SET #Days = DATEDIFF(DAY, #tmpFromDate, #ToDate)
- (CASE WHEN DATEADD(DAY, DATEDIFF(DAY, #tmpFromDate, #ToDate),
#tmpFromDate) > #ToDate THEN 1 ELSE 0 END)
SELECT #FromDate FromDate, #ToDate ToDate,
#Years Years, #Months Months, #Days Days

What about a solution with only date functions, not math, not worries about leap year
CREATE FUNCTION dbo.getAge(#dt datetime)
RETURNS int
AS
BEGIN
RETURN
DATEDIFF(yy, #dt, getdate())
- CASE
WHEN
MONTH(#dt) > MONTH(GETDATE()) OR
(MONTH(#dt) = MONTH(GETDATE()) AND DAY(#dt) > DAY(GETDATE()))
THEN 1
ELSE 0
END
END

declare #birthday as datetime
set #birthday = '2000-01-01'
declare #today as datetime
set #today = GetDate()
select
case when ( substring(convert(varchar, #today, 112), 5,4) >= substring(convert(varchar, #birthday, 112), 5,4) ) then
(datepart(year,#today) - datepart(year,#birthday))
else
(datepart(year,#today) - datepart(year,#birthday)) - 1
end

The following script checks the difference in years between now and the given date of birth; the second part checks whether the birthday is already past in the current year; if not, it subtracts it:
SELECT year(NOW()) - year(date_of_birth) - (CONCAT(year(NOW()), '-', month(date_of_birth), '-', day(date_of_birth)) > NOW()) AS Age
FROM tableName;

SQL Server : DATEDIFF not accurate

I'm trying to retrieve the month difference of two dates but it seems like I can't find a way to get the accurate months.
Here are the queries I tried so far :
SELECT DATEDIFF(month,convert(datetime, '11/05/2015'), convert(datetime, '12/06/2015')) - 1
This will result to 0 which is wrong and when I used another date :
SELECT DATEDIFF(month,convert(datetime, '12/31/2015'), convert(datetime, '01/01/2016')) - 1
This would yield to 0 which is correct.
Leap year must also be considered.

The TSQL is return the correct results as you have written them. As you have it, it is taking the difference of the months between the two dates specified.
SELECT DATEDIFF(month, convert(datetime, '11/05/2015'), convert(datetime, '12/06/2015'))
The difference, in months, between November and December is "1".
However, if you are wanting the difference in terms of every 30 days is 1 month, then you would need to rewrite your query:
declare #daysPerMonth int = 30
SELECT (DATEDIFF(day, convert(datetime, '11/05/2015'), convert(datetime, '12/06/2015')) / #daysPerMonth)
This works if you define the number of days in a month as 30.

Here is a way to visualize what DATEDIFF(month, ...) is doing. Think of a monthly calendar hanging on the wall. For the purposes of this particular SQL function "number" of months between two dates is the number of pages you have to flip to get from one date to the next. It doesn't matter how many days are in each month or whether it's a leap year.
You aren't the first person to be confused about the behavior of the built-in function. If you need to count months by a different method then you'll need to describe the specifics of what you want to accomplish. It's very likely that a solution will be easy to create once you define the problem that needs to be addressed.

In T-SQL you can use CASE:
SELECT DATEDIFF(month, convert(datetime, '11/05/2015'),
convert(datetime, '12/06/2015')) -
CASE
WHEN (MONTH('11/05/2015') > MONTH('12/06/2015')
OR MONTH('11/05/2015') = MONTH('12/06/2015')
AND DAY('11/05/2015') > DAY('12/06/2015'))
THEN 1 ELSE 0
END
Which returns 1 which is correct and:
SELECT DATEDIFF(month, convert(datetime, '12/31/2015'),
convert(datetime, '01/01/2016')) -
CASE
WHEN (MONTH('12/31/2015') > MONTH('01/01/2016')
OR MONTH('12/31/2015') = MONTH('01/01/2016')
AND DAY('12/31/2015') > DAY('01/01/2016'))
THEN 1 ELSE 0
END
Which returns 0 which is correct.

declare
#start date = '20220105',
#end date = '20220406'
select 'Date_Diff_In_3 months' =
case
when datediff(month, #start, #end) < 3
or (datediff(month, #start, #end) = 3 and day(#start) >= day(#end))
then 'yes'
else 'no'
end

SQL - Find working hours between 2 dates excluding weekends

I'm working on a code to get net working days excluding weekends (saturday and sunday). I need this data in days. I've written following 2 functions for it
The first function returns the start time of the date
ALTER FUNCTION day_start
(#dd as datetime)
returns datetime
begin
return cast(floor(cast(#dd as float)) as datetime)
end
The second one does the actual work
alter function networkingdays_hours (#startdate as datetime, #enddate as datetime)
returns float
begin
return
(
SELECT
cast(
(DATEDIFF(dd,#StartDate, #EndDate))
-(DATEDIFF(wk,#StartDate, #EndDate)*2)
-(CASE WHEN DATENAME(dw, #StartDate) ='Sunday'
THEN 1
ELSE 0
END)
-(CASE WHEN DATENAME(dw, #EndDate) ='Saturday'
THEN 1
ELSE 0
END)
+(#EndDate - dbo.day_start(#EndDate))
-(#startdate - dbo.day_start(#startdate))
as float))
END
Example
start time - 8/31/2012 9:22:00 AM, End Time - 9/1/2012 7:14:00 AM, Expected result - 0.911111111, Code output - (-0.08888888)
Please help.

Your function doesn't work in this specific case because Sept 1 is a weekend, and you have indicated that 1 should be subtracted from the result if that is the case.
In the general case, it doesn't work, because there will be an increasing number of special and edge cases that require ever more convoluted logic.
Creating a working days table is a much more flexible solution

TSQL query for Week Comparison

I have a table that has a TASK_START_DATE and TASK_FINISH_DATE Columns of type datetime
I need help with a query that returns all Tasks when the Task: (date = just the date - I think I can do a conversion to the date from datetime on SQL 2008R2, it works fine)
- is within 2 weeks previous of the current date or two weeks after the current date.
Similarly I also need the records whose TaskEnd values are within 2 weeks previous or two weeks before
I've been trying things like which would get tasks where the start date is within the two previous weeks, but I have to do the same for TASK_FINISH_DATE and I think my and's and or's are all jumbled up, any help is appreciated.
Convert(Date, TASK_START_DATE) <= Convert(Date, DateAdd(ww, -2, GetDate()))
Short version:
How do I correctly write a query that combines all records with the TASK_START_DATE OR TASK_END_DATE within two weeks in the future or past, i.e.
Select Task_ID, TASK_NAME, TASK_START_DATE, TASK_END_DATE
where
???

You can add days to your date for comparision:
Select * from Table
Where column between getdate()-14 and getdate()+14

You don't need to use "Convert" function. "GetDate" function returns datetime value and your columns' types are datetime. You can add day number directly like this:
Select * from Table
Where (TASK_START_DATE between getdate() - 14 and getdate() + 14)
or (TASK_FINISH_DATE between getdate() - 14 and getdate() + 14)

You can declare variables or have the comparison dates right in the where clause. I use GETDATE() to get the date/time for right now as it returns a DATETIME object. Then I use DATEADD to adjust it for days, months, years, etc, and then you have to convert it to a DATE before sticking it in a variable of type DATE. Note in the DATEADD method I pass in the adjustment type (D = days), then adjust it + or - 14 days.
Alternatively you could just use 14 days ago to the minute if you don't do the DATE conversions...you'd have to remove the converts from the variable declarations as well as the where clause. Depends on the results you want though.
DECLARE #twoWeeksAgo DATE = CONVERT(DATE, DATEADD(D, -14, GETDATE()));
DECLARE #twoWeeksAhead DATE = CONVERT(DATE, DATEADD(D, 14, GETDATE()));
SELECT
Task_ID,
TASK_NAME,
TASK_START_DATE,
TASK_END_DATE
FROM
TABLE
WHERE
CONVERT(DATE, TASK_START_DATE) BETWEEN #twoWeeksAgo AND #twoWeeksAhead
OR CONVERT(DATE, TASK_END_DATE) BETWEEN #twoWeeksAgo AND #twoWeeksAhead
Also note that the BETWEEN operator in the WHERE clause is inclusive, meaning it will include records where the TASK_START_DATE is equal to the dates held by the variables. If you wanted to exclude records with the same value as #twoWeeksAhead, for example, you would have to use something like
WHERE
(CONVERT(DATE, TASK_START_DATE) >= #twoWeeksAgo
AND CONVERT(DATE, TASK_START_DATE) < #twoWeeksAhead)
OR (CONVERT(DATE, TASK_END_DATE) >= #twoWeeksAgo
AND CONVERT(DATE, TASK_END_DATE) < #twoWeeksAhead)

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