Modifica più righe in una tabella basata sui risultati di subquery

Question

ho la seguente query:

SELECT 
    stat.mcq_id, 
    ROUND(stat.total_score/stat.num_taken, 2) AS avg_score 
    FROM (
     SELECT 
     user_mcq.mcq_id, 
     SUM(score) AS total_score, 
     COUNT(user_mcq.id) AS num_taken 
     FROM user_mcq 
     INNER JOIN user ON (user.id = user_mcq.user_id) 
     WHERE user.level_id =3 
     AND user_mcq.is_complete =1 
     GROUP BY user_mcq.mcq_id 
    ) AS stat 

Questo produce:

mcq_id avg_score 
1  5.75 
2  9.22 
6  8.81 
7  8.94 
14  7.00 
16  9.46 

desidero utilizzare questo per aggiornare un'altra tabella chiamata mcq usando mcq_id dal risultato in corrispondenza dello mcq.id

Ho provato quanto segue, ma senza successo:

UPDATE mcq SET mcq.avg_score = stats.avg_score FROM (
    SELECT 
    stat.mcq_id, 
    ROUND(stat.total_score/stat.num_taken, 2) AS avg_score 
    FROM (
     SELECT 
     user_mcq.mcq_id, 
     SUM(score) AS total_score, 
     COUNT(user_mcq.id) AS num_taken 
     FROM user_mcq 
     INNER JOIN user ON (user.id = user_mcq.user_id) 
     WHERE user.level_id =3 
     AND user_mcq.is_complete =1 
     GROUP BY user_mcq.mcq_id 
    ) AS stat 
) AS stats 
WHERE mcq.id = stats.mcq_id; 

Questo dà:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'FROM (SELECT stat.mcq_id, ROUND(stat.total_score/stat.num_taken, 2) A' at line 1 

Answer 1

Penso che si possa utilizzare il join con la tabella in grado e aggiornare la colonna come di seguito:

UPDATE mcq, 
     (SELECT 
      stat.mcq_id, 
      ROUND(stat.total_score/stat.num_taken, 2) AS avg_score 
      FROM (SELECT 
        user_mcq.mcq_id, 
        SUM(score) AS total_score, 
        COUNT(user_mcq.id) AS num_taken 
        FROM user_mcq 
        INNER JOIN user ON (user.id = user_mcq.user_id) 
        WHERE user.level_id =3 
        AND user_mcq.is_complete =1 
        GROUP BY user_mcq.mcq_id 
      ) AS stat 
     ) AS stats 
SET mcq.avg_score = stats.avg_score 
WHERE mcq.mcq_id = stats.mcq_id;