Can Not Group By on DATE from Timestamp - sql

Question

I am unable to group by on date from a timestamp column in below query:
CHG_TABLE
+----+--------+----------------+-----------------+-------+-----------+
| Key|Seq_Num | Start_Date | End_Date | Value |Record_Type|
+----+--------+----------------+-----------------+-------+-----------+
| 1 | 1 | 5/25/2019 2.05 | 12/31/9999 00.00| 800 | Insert |
| 1 | 1 | 5/25/2019 2.05 | 5/31/2019 11.12 | 800 | Update |
| 1 | 2 | 5/31/2019 11.12| 12/31/9999 00.00| 900 | Insert |
| 1 | 2 | 5/31/2019 11.12| 6/15/2019 12.05 | 900 | Update |
| 1 | 3 | 6/15/2019 12.05| 12/31/9999 00.00| 1000 | Insert |
| 1 | 3 | 6/15/2019 12.05| 6/25/2019 10.20 | 1000 | Update |
+---+---------+----------------+-----------------+-------+-----------+
RESULT:
+-----+------------------+----------------+-----------+----------+
| Key | Month_Start_Date | Month_End_Date |Begin_Value|End_Value |
+---- +------------------+----------------+-----------+----------+
| 1 | 6/1/2019 | 6/30/2019 | 1700 | 1000 |
| 1 | 7/1/2019 | 7/31/2019 | 1000 | 1000 |
+-----+------------------+----------------+-----------+----------+
Begin_Value : Sum(Value) for Max(Start_Date) < Month_Start_Date -> Should pick up latest date from last month
End_Value : Sum(Value) for Max(Start_Date) <= Month_End_Date -> Should pick up the latest date
SELECT k.key,
dd.month_start_date,
dd.month_end_date,
gendata.value first_value,
gendata.next_value last_value
FROM dim_date dd CROSS JOIN dim_person k
JOIN (SELECT ct.key,
dateadd('day',1,last_day(ct.start_date)) start_date ,
SUM(ct.value),
lead(SUM(ct.value)) OVER(ORDER BY ct.start_date) next_value
FROM (SELECT key,to_char(start_Date,'MM-YYYY') MMYYYY, max(start_Date) start_date
FROM CHG_TABLE
GROUP BY to_char(start_Date,'MM-YYYY'), key
) dt JOIN CHG_TABLE ct ON
dt.start_date = ct.start_date AND
dt.key = ct.key
group by ct.key, to_char(start_Date,'MM-YYYY')
) gendata ON
to_char(dd.month_end_date,'MM-YYYY') = to_char(to_char(start_Date,'MM-YYYY')) AND
k.key = gendata.key;
Error:
start_Date is not a valid group by expression
Related post:
Monthly Snapshot using Date Dimension

Answer 1

Hoping, I understood your question correctly.
You can check below query
WITH chg_table ( key, seq_num, start_date, end_date, value, record_type ) AS
(
SELECT 1,1,TO_DATE('5/25/2019 2.05','MM/DD/YYYY HH24.MI'),TO_DATE('12/31/9999 00.00','MM/DD/YYYY HH24.MI'), 800, 'Insert' FROM DUAL UNION ALL
SELECT 1,1,TO_DATE('5/25/2019 2.05','MM/DD/YYYY HH24.MI'),TO_DATE('5/31/2019 11.12','MM/DD/YYYY HH24.MI'), 800, 'Update' FROM DUAL UNION ALL
SELECT 1,2,TO_DATE('5/31/2019 11.12','MM/DD/YYYY HH24.MI'),TO_DATE('12/31/9999 00.00','MM/DD/YYYY HH24.MI'), 900, 'Insert' FROM DUAL UNION ALL
SELECT 1,2,TO_DATE('5/31/2019 11.12','MM/DD/YYYY HH24.MI'),TO_DATE('6/15/2019 12.05','MM/DD/YYYY HH24.MI'), 900, 'Update' FROM DUAL UNION ALL
SELECT 1,3,TO_DATE('6/15/2019 12.05','MM/DD/YYYY HH24.MI'),TO_DATE('12/31/9999 00.00','MM/DD/YYYY HH24.MI'), 1000, 'Insert' FROM DUAL UNION ALL
SELECT 1,3,TO_DATE('6/15/2019 12.05','MM/DD/YYYY HH24.MI'),TO_DATE('6/25/2019 10.20','MM/DD/YYYY HH24.MI'), 1000, 'Update' FROM DUAL
)
select key , new_start_date Month_Start_Date , new_end_date Month_End_Date , begin_value ,
nvl(lead(begin_value) over(order by new_start_date),begin_value) end_value
from
(
select key , new_start_date , new_end_date , sum(value) begin_value
from
(
select key, seq_num, start_date
, value, record_type ,
trunc(add_months(start_date,1),'month') new_start_date ,
trunc(add_months(start_date,2),'month')-1 new_end_date
from chg_table
where record_type = 'Insert'
)
group by key , new_start_date , new_end_date
)
order by new_start_date
;
Db Fiddle link: https://dbfiddle.uk/?rdbms=oracle_18&fiddle=c77a71afa82769b48f424e1c0fa1c0b6

Answer 2

I am assuming that you are getting an "ORA-00979: not a GROUP BY expression" and this is due to your use of the TO_CHAR(timestamp_col,'DD-MM-YYYY') in the GROUP BY clause.
Adding the TO_CHAR(timestamp_col,'DD-MM-YYYY') to the select side of your statement should resolve this and provide the results you are expecting.
a, b, dateadd('day',1,last_day(timestamp_col)) start_date, TO_CHAR(timestamp_col,'DD-MM-YYYY'), ...```