CREATE TABLE REF_DD (
    REF_ID            BIGINT NOT NULL,
    REF_OBJ1          BIGINT NOT NULL,
    REF_OBJ2          BIGINT NOT NULL,
    REF_OBJ3          BIGINT,
    REF_COUNT         NUMERIC(15,3)
);

ALTER TABLE REF_DD ADD CONSTRAINT PK_REF_DD_1 PRIMARY KEY (REF_ID);
ALTER TABLE REF_DD ADD CONSTRAINT FK_REF_DD_2 FOREIGN KEY (REF_OBJ1) REFERENCES DOCUMENT (DC_ID);
ALTER TABLE REF_DD ADD CONSTRAINT FK_REF_DD_3 FOREIGN KEY (REF_OBJ2) REFERENCES ADDTOVAR (TA_ID);
ALTER TABLE REF_DD ADD CONSTRAINT FK_REF_DD_7 FOREIGN KEY (REF_OBJ3) REFERENCES TOVAR (TV_ID);

select r.ref_obj2,
       sum(iif(r.ref_obj1 = 1076345502001, r.ref_count, 0)) as REF_COUNT,
       sum(iif(r.ref_obj1 = 1076345484001, r.ref_count, 0)) as REF_COUNT2
from ref_dd r
where r.ref_id in (1076345490001, 1076345509001)
group by 1

Plan
PLAN (R ORDER FK_REF_DD_3 INDEX (PK_REF_DD_1, PK_REF_DD_1))
------ Performance info ------
Prepare time = 15ms
Execute time = 2s 766ms

select sum(iif(r.ref_obj1 = 1076345502001, r.ref_count, 0)) as REF_COUNT,
       sum(iif(r.ref_obj1 = 1076345484001, r.ref_count, 0)) as REF_COUNT2
from ref_dd r
where r.ref_id in (1076345490001, 1076345509001)

PLAN (R INDEX (PK_REF_DD_1, PK_REF_DD_1))
------ Performance info ------
Prepare time = 32ms
Execute time = 31ms

Plan
PLAN (R ORDER FK_REF_DD_3 INDEX (PK_REF_DD_1, PK_REF_DD_1))

------ Performance info ------
Prepare time = 32ms
Execute time = 1s 390ms
Avg fetch time = 1 390,00 ms
Current memory = 36 432 656
Max memory = 37 517 688
Memory buffers = 2 048
Reads from disk to cache = 9 638
Writes from cache to disk = 0
Fetches from cache = 9 696

Plan
PLAN SORT ((R INDEX (PK_REF_DD_1, PK_REF_DD_1)))

------ Performance info ------
Prepare time = 15ms
Execute time = 16ms
Avg fetch time = 16,00 ms
Current memory = 36 432 504
Max memory = 37 517 688
Memory buffers = 2 048
Reads from disk to cache = 0
Writes from cache to disk = 0
Fetches from cache = 57

    Index FK_REF_DD_3 (5)
        Depth: 3, leaf buckets: 9634, nodes: 27241787
        Average data length: 0.04, total dup: 27024031, max dup: 97033
        Fill distribution:
             0 - 19% = 0
            20 - 39% = 0
            40 - 59% = 324
            60 - 79% = 1
            80 - 99% = 9309