SELECT
        DC.DC_ID AS DC_ID,
        DC.DC_ID_WHOSE_CD AS DC_ID_WHOSE_CD,
        DC.DC_DATE AS DC_DATE
    FROM
        DOCUMENT DC
    WHERE DC.DC_TYPE = 75
      AND DC.DC_ID_WHOSE_CD IS NOT NULL

Plan
PLAN (DC INDEX (FK_DOCUMENT_9))

------ Performance info ------
Prepare time = 32ms
Execute time = 5s 562ms
Avg fetch time = 0,03 ms
Current memory = 36 238 608
Max memory = 36 255 992
Memory buffers = 2 048
Reads from disk to cache = 12 516
Writes from cache to disk = 0
Fetches from cache = 889 963

ALTER TABLE DOCUMENT ADD CONSTRAINT FK_DOCUMENT_9 FOREIGN KEY (DC_TYPE) REFERENCES DOC_TYPE (DCT_CODE);

Plan
PLAN (DCX ORDER DOCUMENT_IDX2 INDEX (FK_DOCUMENT_5, FK_DOCUMENT_9))
PLAN (DC INDEX (FK_DOCUMENT_9))

ALTER TABLE DOCUMENT ADD CONSTRAINT FK_DOCUMENT_5 FOREIGN KEY (DC_ID_WHOSE_CD) REFERENCES CARD_HOLDERS (CH_ID);
ALTER TABLE DOCUMENT ADD CONSTRAINT FK_DOCUMENT_9 FOREIGN KEY (DC_TYPE) REFERENCES DOC_TYPE (DCT_CODE);