Can't use column alias in GROUP BY - sql

Question

I can run this in mysql with no problem
SELECT
DATE_FORMAT(trans_date, '%Y-%m') month,
COUNTRY, COALESCE(COUNT(*), 0) trans_count,
COALESCE(SUM(CASE WHEN state ='approved' THEN 1 END), 0) approved_count,
COALESCE(SUM(amount), 0) trans_total_amount,
COALESCE(SUM(CASE WHEN state ='approved' THEN amount END), 0) approved_total_amount
FROM
Transactions
GROUP BY
month, COUNTRY
ORDER BY
month;
but the same query doesn't run in Orcale, I can't use GROUP BY using aggregation alias, and I can't aggregate without using GROUP BY.
I can call subquery over subquery or use CTE, but it is just so tedious.
What is a good query for type of issue?

Answer 1

As mentioned in another answer, You can not add aliases in GROUP BY but you can add aliases in ORDER BY. Also, DATE_FORMAT is MySql function. It is TO_CHAR in Oracle.
So your final query should be as following:
SELECT
TO_CHAR(TRANS_DATE, 'YYYY-MM') AS MONTH,
COUNTRY,
COUNT(*) AS TRANS_COUNT,
SUM(CASE WHEN STATE = 'approved' THEN 1 ELSE 0 END) AS APPROVED_COUNT,
SUM(AMOUNT) AS TRANS_TOTAL_AMOUNT,
SUM(CASE WHEN STATE = 'approved' THEN AMOUNT ELSE 0 END) AS APPROVED_TOTAL_AMOUNT
FROM TRANSACTIONS
GROUP BY TO_CHAR(TRANS_DATE, 'YYYY-MM'), COUNTRY
ORDER BY MONTH;

Answer 2

Oracle doesn't support aliases for the GROUP BY. Also, the COALESCE() is unnecessary in this case:
SELECT DATE_FORMAT(trans_date, '%Y-%m') as month, COUNTRY,
COUNT(*) as trans_count,
SUM(CASE WHEN state ='approved' THEN 1 ELSE 0 END) as approved_count,
SUM(amount) as trans_total_amount,
SUM(CASE WHEN state = 'approved' THEN amount ELSE 0 END) as approved_total_amount
FROM Transactions
GROUP BY DATE_FORMAT(trans_date, '%Y-%m'), COUNTRY
ORDER BY month;