This query giving error, While executing this syntax error comes for AS LastYearVolumeBilled - oracle

Question

Error comes on AS LastYearVolumeBilled this line how to add two case when in one select statement
select 'R-1' as Year,
(case when SDBM_MONTH_YR = to_number(extract(year from sysdate) || '04')then
round((sum(SDBM_BILLED_UNITS)/avg(sdbm_billing_days))/1000,2)
end )AS CurrentYearVolumeBilled
FROM t_servicedetail_billing
where SDBM_MONTH_YR= to_number(extract(year from sysdate) || '04')
group by SDBM_MONTH_YR ,
(CASE WHEN SDBM_MONTH_YR = to_number( extract(year from add_months(sysdate,-12)) || '04')
THEN round((sum(SDBM_BILLED_UNITS)/avg(sdbm_billing_days))/1000,2)
END)AS LastYearVolumeBilled
FROM t_servicedetail_billing
where SDBM_MONTH_YR= to_number( extract(year from add_months(sysdate,-12)) || '04')
group by SDBM_MONTH_YR;

Answer 1

These are two different queries, so one option might be to treat them as such by using a CTE (as my example shows) or as subqueries.
WITH
t_curr
AS
( SELECT 'R-1' AS year,
(CASE
WHEN sdbm_month_yr =
TO_NUMBER (EXTRACT (YEAR FROM SYSDATE) || '04')
THEN
ROUND (
(SUM (sdbm_billed_units) / AVG (sdbm_billing_days))
/ 1000,
2)
END) AS currentyearvolumebilled
FROM t_servicedetail_billing
WHERE sdbm_month_yr = TO_NUMBER (EXTRACT (YEAR FROM SYSDATE) || '04')
GROUP BY sdbm_month_yr),
t_last
AS
( SELECT 'R-1' AS year,
(CASE
WHEN sdbm_month_yr =
TO_NUMBER (
EXTRACT (YEAR FROM ADD_MONTHS (SYSDATE, -12))
|| '04')
THEN
ROUND (
(SUM (sdbm_billed_units) / AVG (sdbm_billing_days))
/ 1000,
2)
END) AS lastyearvolumebilled
FROM t_servicedetail_billing
WHERE sdbm_month_yr =
TO_NUMBER (
EXTRACT (YEAR FROM ADD_MONTHS (SYSDATE, -12)) || '04')
GROUP BY sdbm_month_yr)
SELECT a.year, a.currentyearvolumebilled, b.lastyearvolumebilled
FROM t_curr a CROSS JOIN t_last b;
How to add more subqueries (simplified):
with
t_curr_r1 as
(select 'R-1' as year, ... from ...),
t_curr_r2 as
(select 'R-2' as year, ... from ...),
t_curr_r3 as
(select 'R-3' as year, ... from ...),
--
t_last_r1
(select 'R-1' as year, ... from ...),
t_last_r2 as
(select 'R-2' as year, ... from ...),
t_last_r3 as
(select 'R-3' as year, ... from ...),
--
select c1.year, c1.currentyearvolumebilled,
c2.currentyearvolumebilled,
c3.currentyearvolumebilled,
...
l1.lastyearvolumebilled,
l2.lastyearvolumebilled,
l3.lastyearvolumebilled,
...
from t_curr_r1 c1 cross join t_curr_r2 c2
cross join t_curr_r3 c3
...
cross join t_last_r1 l1
cross join t_last_r2 l2
cross join t_last_r3 l3
...

Answer 2

You have repeated your query twice. You don't need a case statement cause you have the same condition in where clause. So the correct query might be -
select 'R-1' as Year,
round((sum(SDBM_BILLED_UNITS)/avg(sdbm_billing_days))/1000,2)
END AS CurrentYearVolumeBilled
FROM t_servicedetail_billing
WHERE SDBM_MONTH_YR = to_number(extract(year from sysdate) || '04')