Trying to convert this SQL query to athena query

Trying to convert this to Athena query special the case statement bit

select 
RegDate,
COALESCE(cast(convert(varchar(7), RegDate, 126)  as varchar(7)), NULL ) as [RegMonthYear]
,DATEPART(month, RegDate) as RegMonth
,DATEPART(year, RegDate) as RegYear
,code
,case 
    when cast(year(RegDate)as nvarchar)
                +case when len(cast(month(RegDate) as nvarchar)) = 1 then '0'+cast(month(RegDate) as nvarchar) 
                      else cast(month(RegDate) as nvarchar) 
                end < '20'+code+'01' 
        then 'Jan'
    when cast(year(RegDate)as nvarchar)
                +case when len(cast(month(RegDate) as nvarchar)) = 1 then '0'+cast(month(RegDate) as nvarchar)
                      else cast(month(RegDate) as nvarchar)
                end > '20'+code+'12' 
        then 'Dec'
        else Convert(char(3), RegDate,0) 
end EditionMonth

,case 
    when cast(year(RegDate)as nvarchar)
            +case when len(cast(month(RegDate) as nvarchar)) = 1 then '0'+cast(month(RegDate) as nvarchar)
                  else cast(month(RegDate) as nvarchar) end < '20'+code+'01' then 1
    when cast(year(RegDate)as nvarchar)
            +case when len(cast(month(RegDate) as nvarchar)) = 1 then '0'+cast(month(RegDate) as nvarchar) 
                  else cast(month(RegDate) as nvarchar) 
            end > '20'+code+'12' then 12
    else DATEPART(m,RegDate) 
end EditionMonthNumber

from Details