How do i transform calendar year column to multiple year to months column based on months column and calendar year columns - sql

Question

I have data like this
id MoYear CalenderYear jan feb mar dec
1 2017 2017 1 2 4 0
1 2017 2018 1 0 6 10
2 2018 2018 80 5 8 22
3 2017 2018 30 12 0 3
Now i want ouput like this
id MOyear jan_17 feb_17 mar_17 dec_17 jan_18 feb_18 mar_18 dec_18
1 2017 1 2 4 0 1 0 6 10
2 2018 null null null null 80 5 8 22
3 2017 null null null null 30 12 0 3
I have calendar year column and months columns, based on the calendar year and months column i need to make multiple year-months columns.
I can get to the solution by unpivoting and then after back to pivot. But, the data is so large it takes a lot of memory. The performance is very bad.

Answer 1

Not sure if this will be better approach but you can achieve your output using case statement as well if you don't want to do pivot/unpivot.
Data Creation:
select 1 as ID, 2017 as MOYEar, 2017 as calenderyear, 1 as Jan, 2 as feb,
4 as mar, 0 as dece into #temp union all
select 1 as ID, 2017 as MOYEar, 2018 as calenderyear, 1 as Jan, 0 as feb,
6 as mar, 10 as dece union all
select 2 as ID, 2018 as MOYEar, 2018 as calenderyear, 80 as Jan, 5 as feb,
8 as mar, 22 as dece union all
select 3 as ID, 2017 as MOYEar, 2018 as calenderyear, 30 as Jan, 12 as feb,
0 as mar, 3 as dece
Query:
Select ID, MOYEar, max(case when calenderyear = '2017' then Jan else null end) as Jan_17,
max(case when calenderyear = '2017' then Feb else null end ) as Feb_17,
max(case when calenderyear = '2017' then Mar else null end ) as Mar_17,
max(case when calenderyear = '2017' then Dece else null end) as Dece_17,
max(case when calenderyear = '2018' then Jan else null end ) as Jan_18,
max(case when calenderyear = '2018' then Feb else null end ) as Feb_18,
max(case when calenderyear = '2018' then Mar else null end ) as Mar_18,
max(case when calenderyear = '2018' then Dece else null end) as Dece_18 from #temp
Group by ID, MOYEar
Output:
ID MOYEar Jan_17 Feb_17 Mar_17 Dece_17 Jan_18 Feb_18 Mar_18 Dece_18
1 2017 1 2 4 0 1 0 6 10
3 2017 NULL NULL NULL NULL 30 12 0 3
2 2018 NULL NULL NULL NULL 80 5 8 22