Calculating the sum of annual amounts when frequencies of payments differ - sql

Question

I'm currently trying to write a select statement which calculates the Annual sum in one single column.
The problem I am facing is that there are several different payment frequencies e.g. I would have to multiply a monthly amount by 12 to get the annual, quarterly by 4, semi annual by 2 etc.
I have written a statement below which does this, however it demands that I group by the frequency and amount fields, which gives the undesired result.
select (case when Frequency='month' then SUM(cast(Amount as decimal(10,2))*12)
else (case when Frequency='quarter' then SUM(cast(Amount as decimal(10,2))*4)
else (case when Frequency='year' then SUM(cast(Amount as decimal(10,2))*1)
else (case when Frequency='six months' then SUM(cast(Amount as decimal(10,2))*2) end)
end)
end) end) as 'Total Annual Amount'
from Table group by Frequency
I understand I maybe barking up the wrong tree as far as solving this problem, but the above is the closest I have gotten.
Hopefully I have been descriptive enough, if you need me to elaborate further please let me know

Answer 1

Try moving your sum outside of your case:
select
sum (case when Frequency='Month' then (cast(amount as decimal(10,2))*12
when Frequency='quarter' then...
end) as [Total Annual Amount]

Answer 2

You can also use WITH AS (assuming ORACLE)...
WITH dmap AS
( select 'Month' as duration, 12 as mult from dual
UNION
select 'Year' as duration, 1 as mult from dual
UNION
select 'Quater' as duration, 4 as mult from dual
UNION
select 'six months' as duration, 2 as mult from dual
)
select sum(cast(Amount as decimal(10,2)) * mult)
from tab, dmap
where duration = frequency;