Question

我有一张桌子，上面有活动嘉宾的数据。我可以使用此查询检索已有人（membersAttended）的人数：

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;

要检索我使用的成员总数（totalMembers）：

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

要获得参与总成员的百分比值（totalPercent）成员，我使用PHP来进行两次查询，然后计算如下：< / p>
```
$totalPercent = number_format(($membersAttended/$totalMembers*100),2);
```

我尝试将两个查询和百分比计算以类似的方式组合到下面，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;

我也尝试扩展列：

    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 clause'
中的未知列'g.event_id'

如何将这些SQL / PHP查询/计算合并到一个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;

结合并使用来自两个不同表

1 个答案: