SQL - Use of PARSENAME() function

Sometimes when we have pivoted value in excel or csv with title as 'Column 1','Column 2',...'Column n'. But in the meantime, those columns means the dates like 1980-01-01, 1980-02-01. After unpivot the data into sql , the data will be like this:
API               date_string Product
053-29070 Column 112 Oil
053-29070 Column 113 Oil
053-29070 Column 118 Oil
053-29070 Column 172 Oil
053-29070 Column 173 Oil
053-29070 Column 177 Oil
053-29070 Column 178 Oil
053-29070 Column 19 Oil
Then how do we know the corresponding year and month?

So here is the trick. Function PARSENAME() can get the specific part of a string delimited by a delimiter. so
for SELECT PARSENAME(12.3,1), you will get 3,
for SELECT PARSENAME(13%12,1), you will get 1

so by using this function together with remainder function, we can get the month of the data.
by using some tricks with number/12, we can get the year of the data.

date_string	date_int	month_indicator	year_indicator	date_int_plus
Column 1	1	1	0	2
Column 2	2	2	0	3
Column 3	3	3	0	4
Column 4	4	4	0	5
Column 5	5	5	0	6
Column 6	6	6	0	7
Column 7	7	7	0	8
Column 8	8	8	0	9
Column 9	9	9	0	10
Column 10	10	10	0	11
Column 11	11	11	0	12
Column 12	12	0	1	13
Column 13	13	1	1	14
Column 14	14	2	1	15
Column 15	15	3	1	16
Column 16	16	4	1	17
Column 17	17	5	1	18
Column 18	18	6	1	19
Column 19	19	7	1	20
Column 20	20	8	1	21
Column 21	21	9	1	22
Column 22	22	10	1	23
Column 23	23	11	1	24

--------------------------update production_month---------------------------------------

so we can   set  production_month = 

     case      when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 1 then 1

                  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 2 then 2

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 3 then 3

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 4 then 4

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 5 then 5

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 6 then 6

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 7 then 7

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 8 then 8

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 9 then 9

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 10 then 10

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 11 then 11

  when PARSENAME(cast(replace(date_string,'Column ','') as int)%12,1) = 0 then 12

  else null 

  end

--------------------------update production_year---------------------------------------

IF OBJECT_ID('tempdb..#tbl_prod') IS NOT NULL DROP TABLE #tbl_prod

select distinct cast(PARSENAME(cast(replace(date_string,'Column ','') as int)/12,1) as int) as year_indicator, cast(replace(date_string,'Column ','') as int) +1 as date_int_plus

into #tbl_prod

from XXXX with (nolock)

DECLARE @counter int = 0; 

WHILE @counter <= (select max(cast(replace(date_string,'Column ','') as int)) from XXXX)

BEGIN

update a

set production_year = 1980 + @counter

from XXXX a ,#tbl_prod b

where b.year_indicator = @counter and cast(replace(a.date_string,'Column ','') as int) =               

                  b.date_int_plus and a.api <> '' and a.volume <> 0 and a.volume is not null ;

SET @counter = @counter + 1;

END

--only column 1 is not assigned a year

update XXXX

set production_year = 1980

where date_string = 'Column 1' and api <> '' and volume is not null and volume <> 0;

Or just the easiest way. Use SELECT DATEADD(MONTH,+1,getdate()) to get the date.