select all with other parameters in db2
any not aggregated column must be included in GROUP BY

SELECT COL1, COL2 ,SUM(total_request_count) AS total_calls  FROM API_REQUEST_SUMMARY GROUP BY COL1, COL2


alternative if many columns for GROUP BY

SELECT T1.*, T2.total_calls FROM API_REQUEST_SUMMARY T1 LEFT JOIN
(SELECT GROUP_COLUMN, SUM(total_request_count) AS total_calls  FROM API_REQUEST_SUMMARY GROUP BY GROUP_COLUMN) T2 ON T1.GROUP_COLUMN = T2.GROUP_COLUMN


it is my work solution, may be other present as well