WITH T
AS (SELECT
        a.ID
    FROM
        articles a
    ORDER BY A.ID DESC
    FETCH FIRST 100 ROWS ONLY)
SELECT
    a.ID, DS.RND
FROM
    (SELECT
         ID,
         RAND() AS RND,
         -- оконная функция заставляет материализовасться результат
         COUNT(*) OVER() AS N
     FROM
         T) DS
JOIN articles a ON a.ID=DS.ID
ORDER BY DS.RND
FETCH FIRST 10 ROWS ONLY

WITH DS
AS (SELECT
        a.ID,
        -- вот это материализует точно
        (SELECT RAND() FROM RDB$DATABASE) AS RND 
    FROM
        articles a
    ORDER BY A.ID DESC
    FETCH FIRST 100 ROWS ONLY)
SELECT
    a.ID, DS.RND AS RND1, DS.RND AS RND2
FROM DS
JOIN articles a ON a.ID=DS.ID
ORDER BY DS.RND