合并并对来自两个不同表的SQL值使用算术运算

Question

1. 我有一张桌子，上面有活动客人的数据。 我可以通过此查询检索已出席的人数（ membersAttended ）：

    SELECT COUNT(DISTINCT g.`name1`) AS `membersAttended` FROM `tmc_doorapp_guests` g LEFT JOIN `tmc_doorapp_events` e ON e.`id` = g.`event_id` WHERE `name1` REGEXP '^[0-9]+$' AND e.`date` > DATE_SUB(NOW(), INTERVAL 30 DAY) AND g.`checkin` = 1; 

2. 要检索成员总数（ totalMembers ），请使用：

    SELECT COUNT(DISTINCT `id`) AS `totalMembers` FROM `tmc_users`; 

3. 为了获得已参加所有成员的成员的百分比值 （ totalPercent ），我使用PHP进行了两个查询，然后进行如下计算：

    $totalPercent = number_format(($membersAttended/$totalMembers*100),2); 

---

我尝试以下面类似的方式结合两个查询和百分比计算，但是没有运气：

    SELECT COUNT(DISTINCT g.`name1`) AS `membersAttended`,
        COUNT(DISTINCT m.`id`) AS `totalMembers`,
        (`membersAttended` * 100 / `totalMembers`) AS `totalPercent`
        FROM `tmc_doorapp_guests` g, `tmc_users` m
        LEFT JOIN `tmc_doorapp_events` e
        ON e.`id` = g.`event_id`
        WHERE `name1` REGEXP '^[0-9]+$'
        AND e.`date` > DATE_SUB(NOW(), INTERVAL 30 DAY)
        AND g.`checkin` = 1;

我还尝试扩展列：

    SELECT COUNT(DISTINCT g.`name1`) AS `membersAttended`,
        COUNT(DISTINCT m.`id`) AS `totalMembers`,
        (COUNT(DISTINCT g.`name1`) * 100 / COUNT(DISTINCT m.`id`)) AS `totalPercent`
        FROM `tmc_doorapp_guests` g, `tmc_users` m
        LEFT JOIN `tmc_doorapp_events` e
        ON e.`id` = g.`event_id`
        WHERE `name1` REGEXP '^[0-9]+$'
        AND e.`date` > DATE_SUB(NOW(), INTERVAL 30 DAY)
        AND g.`checkin` = 1;

这给了我错误：

错误代码：1054。“ on子句”中的未知列“ g.event_id”

如何将这些SQL / PHP查询/计算组合到一个SQL查询中？

Answer 1

您可以使用子查询：

SELECT COUNT(DISTINCT g.`name1`) AS `membersAttended`,
       (SELECT COUNT(DISTINCT `id`) FROM `tmc_users`) AS `totalMembers`,
       COUNT(DISTINCT g.`name1`) * 100 / (SELECT COUNT(DISTINCT `id`)
                                          FROM `tmc_users`) AS `totalPercent`
FROM `tmc_doorapp_guests` g
LEFT JOIN `tmc_doorapp_events` e
ON e.`id` = g.`event_id`
WHERE `name1` REGEXP '^[0-9]+$'
AND e.`date` > DATE_SUB(NOW(), INTERVAL 30 DAY)
AND g.`checkin` = 1;