T-SQL date pickup - sql

Question

I am looking for some T-SQL code that should pick the date which is "One Year back from current date (at the same time last Sunday in the month of January)".
I have some T-SQL code which is being used in SQL Server 2014:
select
convert(varchar(10), DATEADD(day, DATEDIFF(day, '19000107', DATEADD(month, DATEDIFF(MONTH, 0, CONVERT(date, CONVERT(VARCHAR(4), (CASE WHEN MONTH(GetDate()) = 1 THEN CONVERT(VARCHAR(4), GetDate(), 112) - 1 ELSE CONVERT(VARCHAR(4), GetDate(), 112) END), 112) + '0101')), 30)) / 7 * 7, '19000107'), 120)
The above code picks the date for current year's (last Sunday in January month). But I want T-SQL code to pick last year's (last Sunday's date in January month) date.
In detail - I want T-SQL code to produce expected result from below table
Current day Expected result
---------------------------------------
2017-02-05 2016-01-31
2017-01-05 2015-01-25
2018-02-19 2017-01-29
2018-01-19 2016-01-31
2019-02-28 2018-01-28
Please note always year starts from "Last Sunday in January month".

Answer 1

There will be more concise solutions, but when we assume that your code is time-tested and robust, I would simply substitute the GETDATE() by an expression that is now minus one year:
DATEADD(year, -1, GETDATE())
Thus:
SELECT
convert(varchar(10), DATEADD(day, DATEDIFF(day, '19000107', DATEADD(month, DATEDIFF(MONTH, 0, CONVERT(date, CONVERT(VARCHAR(4), (CASE WHEN MONTH(DATEADD(year,-1,GetDate())) = 1 THEN CONVERT(VARCHAR(4), DATEADD(year,-1,GetDate()), 112) - 1 ELSE CONVERT(VARCHAR(4), DATEADD(year,-1,GetDate()), 112) END), 112) + '0101')), 30)) / 7 * 7, '19000107'), 120)

Answer 2

If you have a calendar table, you can skip the first CTE (and probably the MAXRECURSION option) and just use the calendar table. Hopefully this is clearly correct:
declare #today date
set #today = CURRENT_TIMESTAMP
;With Dates as (
select CONVERT(date,'19000101') as d
union all
select DATEADD(day,1,d) from Dates where d < '21000101'
), ApplicableSundays as (
select d,ROW_NUMBER() OVER (ORDER BY d desc) as rn
from Dates
where d < #today and
DATEPART(month,d) = 1 and
DATEPART(weekday,d) = DATEPART(weekday,'20150913') and --Any known Sunday
DATEPART(day,d) between 25 and 31
)
select d
from ApplicableSundays where rn = 2
option (maxrecursion 0)
Dates generates all dates in the 20th and 21st centuries, which is hopefully flexible enough for your purposes.
ApplicableSundays filters these rows down to dates which occur before #today, are in January, are a Sunday (using a known-good date rather than relying on any particular DATEFIRST setting) and falls between the 25th and the 31st of that month.
We then pick the second most recent of these dates, which must be the start of last year, if our years start on the last Sunday of each January.
If you're working against a table full of dates for which you wish to find this "start of last year" value, you would introduce it as a join in the ApplicableDates CTE and partition the ROW_NUMBER() aggregate using those values, so that you can find all of the Sundays in parallel.

Answer 3

This will seclude the columns with the data .
Please give it a try let me know. Thanks.
select
convert(varchar(10), DATEADD(day, DATEDIFF(day, '19000107', DATEADD(month, DATEDIFF(MONTH, 0, CONVERT(date, CONVERT(VARCHAR(4), (CASE WHEN MONTH(GetDate()) = 1 THEN CONVERT(VARCHAR(4), GetDate(), 112) - 1 ELSE CONVERT(VARCHAR(4),
GetDate(), 112) END), 112) + '0101')), 30)) / 7 * 7, '19000107'), 120) AS CurrentDay , convert(varchar(10), DATEADD(day, DATEDIFF(day, '19000107', DATEADD(month, DATEDIFF(MONTH, 0, CONVERT(date, CONVERT(VARCHAR(4), (CASE WHEN MONTH(DATEADD(year,-1,GetDate())) = 1 THEN CONVERT(VARCHAR(4), DATEADD(year,-1,GetDate()), 112) - 1 ELSE CONVERT(VARCHAR(4),
DATEADD(year,-1,GetDate()), 112) END), 112) + '0101')), 30)) / 7 * 7, '19000107'), 120) as ExpectedResult