Query group by in h2 works but not in Oracle DB

i have a query like the following:

SELECT
  sum(field1) as t1.sum_f1,
  (select count(*) from table2) as count_t2,
  t1.f2
FROM 
  t1
GROUP BY 
  t1.f2

This query is getting executed by a javax.persistence.EntityManager java istance.
EntityManager runs the query in an Oracle DB.
I've written Mockito test, configured with H2 in memory database.

The problem is the following:
When the same query is getting executed by a Mockito test (that uses H2 as DB), it works fine.
When i run my java application (that uses OracleDB as DB) it gives me ERROR: ORA-00979.

I think it expects count_t2 to be in the group by field list but this is not permitted cause inner queries are processed after gruop by (so count_t2 is not visible at "group by - time") in SQL.

How can i solve it?
Thanks.

Move the calculation to the FROM clause:

SELECT SUM(field1) as t1.sum_f1, t2.count_t2, t1.f2
FROM t1 CROSS JOIN
     (SELECT COUNT(*) as count_t2 FROM  table2) t2
GROUP BY t1.f2, t2.count_t2;

Subqueries with aggregation queries can be tricky for query parsers.

I finally found the way to let it works.

SELECT
  sum(field1) as t1.sum_f1,
  count((select 1 from table2)) as count_t2,
  t1.f2
FROM 
  t1
GROUP BY 
  t1.f2  

In this way projection fields are "SUM, COUNT" and the aggregation field.
This query works fine in both H2 and ORACLE DB.