Pokročilé MySQL:Najděte korelace mezi odpověďmi na průzkum

Nemáte po ruce instanci k otestování, můžete se podívat, zda to má správné výsledky:

select
        poll_id,
        option_id,
        ((psum - (sum1 * sum2 / n)) / sqrt((sum1sq - pow(sum1, 2.0) / n) * (sum2sq - pow(sum2, 2.0) / n))) AS r,
        n
from
(
    select 
        poll_id,
        option_id,
        SUM(score) AS sum1,
        SUM(score_rev) AS sum2,
        SUM(score * score) AS sum1sq,
        SUM(score_rev * score_rev) AS sum2sq,
        SUM(score * score_rev) AS psum,
        COUNT(*) AS n
    from
    (
            select 
                responses.poll_id, 
                responses.option_id,
                CASE 
                    WHEN user_resp.user_id IS NULL THEN SELECT 0
                    ELSE SELECT 1
                END CASE as score,
                CASE 
                    WHEN user_resp.user_id IS NULL THEN SELECT 1
                    ELSE SELECT 0
                END CASE as score_rev,
            from responses left outer join 
                    (
                        select 
                            user_id
                        from 
                            responses 
                        where
                            poll_id = 1 and 
                            option_id = 2
                    )user_resp  
                        ON (user_resp.user_id = responses.user_id)
    ) temp1 
    group by
        poll_id,
        option_id
)components