重新使用父语句中的嵌套SQL语句在MySQL

Question

我有以下SQL代码;

SELECT a.*, b.maxDate as last_payment_date, c.package as payment_for_package, (SELECT COUNT(id) FROM uploads WHERE user = a.id) AS upload_count 
       FROM users a 
        INNER JOIN payments c 
         ON a.id = c.user_id 
        INNER JOIN 
        (
         SELECT user_id, MAX(date) maxDate, period 
         FROM payments 
         GROUP BY user_id 
        ) b ON c.user_id = b.user_id AND 
          c.date = b.maxDate 

       WHERE a.package = 1 
       AND b.maxDate < $twomonths 
       AND (SELECT COUNT(id) FROM uploads WHERE user = a.id) > 10 
       AND b.period = 1 
       ORDER BY b.maxDate ASC 
       LIMIT 50 

正如你可以看到我使用嵌套的语句(SELECT COUNT(id) FROM uploads WHERE user = a.id)两次，我想知道如果有一种方法可以重新使用该语句，以提高性能？我已经使用别名upload_count尝试，但你不能在WHERE条款使用别名。感谢帮助

Answer 1

刚刚加入到子查询和结果进行相关性：

SELECT 
    a.*, 
    b.maxDate as last_payment_date, 
    c.package as payment_for_package, 
    upload_counts.upload_count 

FROM users a 

INNER JOIN payments c 
    ON a.id = c.user_id 

INNER JOIN 
(
    SELECT user_id, MAX(date) maxDate, period 
    FROM payments 
    GROUP BY user_id 
) b ON c.user_id = b.user_id AND 
     c.date = b.maxDate 

INNER JOIN 
(
    SELECT user, COUNT(id) AS upload_count 
    FROM uploads 
    GROUP BY user 
) upload_counts ON upload_counts.user = a.id 

WHERE a.package = 1 
AND b.maxDate < $twomonths 
AND upload_counts.upload_count > 10 
AND b.period = 1 

ORDER BY b.maxDate ASC 
LIMIT 50;