Question

在下面的查询中它返回12条记录，而来自from子句的查询（作为t）返回18条记录，任何人都可以帮助查询中的问题是什么？

SELECT count(abc.id) as total_this_month,t.* 
FROM email_details abc
JOIN
(SELECT count(email_details.id) as total_emails,MAX(`email_details`.email_date) as email_date1, `email_details`.* FROM (`cld_users` join email_details on email_details.fk_user_id = cld_users.id) GROUP BY `email_details`.`email_title` ORDER BY `email_details`.`email_date` DESC) as t 
ON abc.email_title = t.email_title
where (MONTH(abc.email_date)=MONTH(NOW()) AND YEAR(abc.email_date)=YEAR(NOW()))
group by  t.email_title
ORDER BY t.`email_date` DESC

Answer 1

在您的查询中，指定

where (MONTH(abc.email_date)=MONTH(NOW()) AND YEAR(abc.email_date)=YEAR(NOW()))

但是在子查询（返回18个结果的那个）中，您有6封电子邮件，其中一个月不是2014年12月。这些电子邮件无法通过明确排除它们的查询返回。

你也想要那些电子邮件，所以你得到18个结果？删除不包括它们的WHERE子句：

SELECT Count(abc.id) AS total_this_month,
       t.*
FROM   email_details abc
       JOIN (SELECT Count(email_details.id)         AS total_emails,
                    Max(`email_details`.email_date) AS email_date1,
                    `email_details`.*
             FROM   (`cld_users`
                     JOIN email_details
                       ON email_details.fk_user_id = cld_users.id)
             GROUP  BY `email_details`.`email_title`
             ORDER  BY `email_details`.`email_date` DESC) AS t
         ON abc.email_title = t.email_title
GROUP  BY t.email_title
ORDER  BY t.`email_date` DESC

从那里开始，如果您想计算当月的电子邮件，只需替换：

SELECT Count(abc.id) AS total_this_month,

与

SELECT SUM(CASE WHEN MONTH(abc.email_date)=MONTH(NOW()) AND YEAR(abc.email_date)=YEAR(NOW()) THEN 1 ELSE 0 END) AS total_this_month,

我的查询中有什么错误？

1 个答案: