CREATE TABLE test_filters(
    field1 INTEGER
  , field2 INTEGER
  , field3 INTEGER
  , field4 INTEGER
  , field5 INTEGER
);

CREATE PROCEDURE fill_test_filters(p_count INTEGER)

  DEFINE i INTEGER;

  INSERT INTO test_filters(
    field1, field2, field3, field4, field5
  ) VALUES (
     1 ,  2 ,  3 ,  4 ,  5 
  );

  FOR i =  1  TO p_count 
    INSERT INTO test_filters(
      field1, field2, field3, field4, field5
    ) SELECT field1, field2 *  2 , field3 *  3 , field4 *  4 , field5 *  5 
        FROM test_filters;
  END FOR
END PROCEDURE;

EXECUTE PROCEDURE fill_test_filters( 20 ); -- МБ записей

CREATE INDEX idx_tst_field1 ON test_filters(field1);
CREATE INDEX idx_tst_field2 ON test_filters(field2);
CREATE INDEX idx_tst_field3 ON test_filters(field3);
CREATE INDEX idx_tst_field4 ON test_filters(field4);
CREATE INDEX idx_tst_field5 ON test_filters(field5);

CREATE INDEX idx_tst_field23 ON test_filters(field2, field3);

UPDATE STATISTICS HIGH FOR TABLE test_filters;

CREATE PROCEDURE run_test_filters(
    p_filter1 INTEGER
  , p_filter2 INTEGER
  , p_filter3 INTEGER
  , p_filter4 INTEGER
  , p_filter5 INTEGER
) RETURNING
    INT -- кол-во записей
  ;

  DEFINE v_cnt INTEGER;

  LET v_cnt = (
    SELECT COUNT(*)
      FROM test_filters
        WHERE (field1 = p_field1 OR p_field1 IS NULL)
          AND (field2 = p_field2 OR p_field2 IS NULL)
          AND (field3 = p_field3 OR p_field3 IS NULL)
          AND (field4 = p_field4 OR p_field4 IS NULL)
          AND (field5 = p_field5 OR p_field5 IS NULL)
  );

  RETURN v_cnt;
END PROCEDURE;

Estimated Cost: 175804
Estimated # of Rows Returned: 1

  1) tolik.test_filters: SEQUENTIAL SCAN

        Filters: 
(((((tolik.test_filters.field5 = '<VAR>' OR '<VAR>' IS NULL ) 
AND (tolik.test_filters.field4 = '<VAR>' OR '<VAR>' IS NULL ) ) 
AND (tolik.test_filters.field3 = '<VAR>' OR '<VAR>' IS NULL ) ) 
AND (tolik.test_filters.field2 = '<VAR>' OR '<VAR>' IS NULL ) ) 
AND (tolik.test_filters.field1 = '<VAR>' OR '<VAR>' IS NULL ) )