在SQL上转换为ISO周到月的日期

Question

I've searched on almost every question but haven't come with what I need, so here it goes:

I need to convert a date in the format of 'yyyyww' (where 'ww' is the iso week of the year) to 'yyyymm' (where 'mm' is the month of the year).

So, for example, I have the date 201725 (which is year 2017, ISO week 25) to be displayed as 201706, since the ISO week 25 is on June of the same year.

Answer 1

Use a combination of the LEFT , CONVERT & DATEADD Functions.

SELECT LEFT(CONVERT(varchar, DATEADD(week, yourfield % 100 - 1, DATEADD(year, yourfield / 100 - 1900, 0)),112),6)
FROM yourtable

Input

201722
201733
201725

Output

201705
201708
201706

SQL Fiddle: http://sqlfiddle.com/#!6/00eaa/7/0

Answer 2

This is a bit strange for output because you can get the same value for more than 1 week but I will leave that up to you to sort out.

This produces the desired output stated for the input provided.

declare @YourValue varchar(10) = '201725'

select left(replace(convert(varchar(10), dateadd(week, convert(int, right(@YourValue, 2)), left(@YourValue, 4) + '0101'), 102), '.', ''), 6)