In case you have your own slow SQL query, you can optimize it automatically here.
For the query above, the following recommendations will be helpful as part of the SQL tuning process.
You'll find 3 sections below:
ALTER TABLE `C` ADD INDEX `c_idx_code_closed_rcvd_dt` (`CODE`,`CLOSED`,`RCVD_DT`);
ALTER TABLE `D` ADD INDEX `d_idx_system_code` (`SYSTEM`,`CODE`);
SELECT
C.REF_CD
FROM
C
INNER JOIN
D
ON C.SYSTEM = D.SYSTEM
WHERE
C.CODE = '123'
AND D.CODE IS NOT NULL
AND C.CLOSED = 'N'
AND C.RCVD_DT >= TO_DATE('12/01/2017', 'MM/DD/YYYY')
AND C.RCVD_DT <= TO_DATE('12/04/2017', 'MM/DD/YYYY')
AND SUBSTR(C.SSN, 7, 3) >= D.FROM
AND SUBSTR(C.SSN, 7, 3) <= D.TO