demo, MySQL - rextester

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#MySQL 5.7.12
#please drop objects you've created at the end of the script 
#or check for their existance before creating
#'\\' is a delimiter

DROP TABLE IF EXISTS user_answers;
CREATE TABLE user_answers (id int, question_id int, user_id int, answer_id int, create_date datetime);
INSERT INTO user_answers (id, question_id, user_id, answer_id, create_date)
VALUES
    (1,  1, 9, 5,  null),
    (2,  2, 8, 7,  null),
    (3,  1, 1, 3,  null),
    (4,  3, 4, 20, null),
    (5,  1, 4, 5,  null),
    (6,  4, 3, 25, null),
    (7,  2, 7, 5,  null),
    (8,  4, 9, 26, null),
    (9,  2, 5, 8,  null),
    (10, 1, 1, 5,  null);

SET @row_num = 0;
SET @q_id = NULL;

SELECT
    t.id,
    t.question_id,
    t.user_id,
    t.answer_id,
    t.create_date
FROM
(
    SELECT 
        @row_num:=CASE WHEN @q_id = question_id THEN @row_num + 1 ELSE 1 END AS rn,
        @q_id:=question_id as question_id,
        id,
        user_id,
        answer_id,
        create_date
    FROM
        user_answers
    ORDER BY question_id, id
) t
WHERE t.rn <= 2
ORDER BY t.question_id, t.id;


absolute service time: 0,46 sec