oracle query to retrieve the date of the highest value which are grouped by month and year - sql

Question

Data looks similar to this..
Here I need to retrieve the highest amount by grouping them by month and year but I couldn't retrieve the exact date of the highest amount....
The code I tried for the highest amount is ...
SELECT ACCT_ID AS ACCOUNT_ID,
COUNT(TRANS_AMOUNT) AS NUMBER_OF_TRANSACTION,
Sum(Trans_Amount) As Transaction_Amount,
To_Char( Trans_Date, 'MON-YYYY') As Month_Date,
Max(Trans_Amount) As Highest
From Trans_Amt
group by ACCT_ID, To_Char( Trans_Date, 'MON-YYYY');
And this worked but I could not retrieve the date here. If I try for the date I get "not a group by variable" error ...

Answer 1

Group by account and month(I used trunc at month level).
Select max(amount) for amount and use keep dense_rank first to get the date of maximum amount:
SELECT
ACCT_ID AS ACCOUNT_ID,
trunc(Trans_Date, 'MM') As Month_Date,
max(trans_date) keep (dense_rank first order by trans_amount desc) as trans_date
Max(Trans_Amount) As Highest
FROM Trans_Amt
GROUP BY
ACCT_ID, trunc(Trans_Date, 'MM');

Answer 2

with t as (
select 1000 ACCT_ID, to_date('11-JAN-2000', 'dd-MM-yyyy') TRANS_DATE, 201 TRANS_AMOUNT from dual union all
select 1000, to_date('22-JAN-2000', 'dd-MM-yyyy'), 209 from dual union all
select 1000, to_date('31-JAN-2000', 'dd-MM-yyyy'), 4504 from dual union all
select 1000, to_date('10-FEB-2000', 'dd-MM-yyyy'), 487 from dual union all
select 1001, to_date('10-FEB-2000', 'dd-MM-yyyy'), 4287 from dual union all
select 1001, to_date('17-FEB-2000', 'dd-MM-yyyy'), 4501 from dual union all
select 1001, to_date('22-FEB-2000', 'dd-MM-yyyy'), 1209 from dual union all
select 1000, to_date('22-FEB-2000', 'dd-MM-yyyy'), 4550 from dual union all
select 1001, to_date('23-FEB-2000', 'dd-MM-yyyy'), 120 from dual union all
select 1001, to_date('26-FEB-2000', 'dd-MM-yyyy'), 245 from dual union all
select 1000, to_date('28-FEB-2000', 'dd-MM-yyyy'), 4500 from dual union all
select 1000, to_date('08-MAR-2000', 'dd-MM-yyyy'), 256 from dual union all
select 1001, to_date('08-MAR-2000', 'dd-MM-yyyy'), 2561 from dual union all
select 1000, to_date('24-MAR-2000', 'dd-MM-yyyy'), 987 from dual union all
select 1001, to_date('24-MAR-2000', 'dd-MM-yyyy'), 75000 from dual union all
select 1000, to_date('31-MAR-2000', 'dd-MM-yyyy'), 1100 from dual union all
select 1001, to_date('31-MAR-2000', 'dd-MM-yyyy'), 11000 from dual union all
select 1001, to_date('04-APR-2000', 'dd-MM-yyyy'), 4287 from dual union all
select 1000, to_date('04-APR-2000', 'dd-MM-yyyy'), 487 from dual union all
select 1001, to_date('12-APR-2000', 'dd-MM-yyyy'), 1209 from dual union all
select 1001, to_date('14-APR-2000', 'dd-MM-yyyy'), 1092 from dual union all
select 1001, to_date('20-APR-2000', 'dd-MM-yyyy'), 1245 from dual union all
select 1000, to_date('20-APR-2000', 'dd-MM-yyyy'), 7500 from dual union all
select 1000, to_date('22-APR-2000', 'dd-MM-yyyy'), 1205 from dual union all
select 1000, to_date('26-APR-2000', 'dd-MM-yyyy'), 245 from dual
)
select
*
from
t t
where
not exists(
select
*
from
t n
where
trunc(t.TRANS_DATE, 'mm') = trunc(n.TRANS_DATE, 'mm')
and n.TRANS_AMOUNT > t.TRANS_AMOUNT
and t.ACCT_ID = n.ACCT_ID
)
order by
t.TRANS_DATE, t.ACCT_ID
Output