Mysql如何获取子查询的列名？

Question

假设我有以下查询：

SELECT
    c.id AS 'course_id',u.id as 'user_id',c.round,u.first_name as name,u.last_name as family_name,u.`father_name`,u.`tazkera_id` as tazkira,c.`no` as class_ID,tc.province,tc.village,tl.id as training_provider_id,
    CASE c.`shift`
        WHEN 1 THEN 'Morning'
        WHEN 2 THEN 'Afternoon'
    END as shift,
    c.`start_date`as start_date,
    sa.participant_id,
    DATE_FORMAT(ca.`date`,'%Y-%m-%d') as attendence,
    CASE sa.`precence` 
        WHEN 0 THEN 'A' 
        WHEN 1 THEN 'P' 
    END as attendence_status 
FROM `users` AS u
LEFT JOIN `provinces` as pu On pu.`province_code` = u.`province_code`
LEFT JOIN `districts` as du on du.`district_code` = u.`district_code`

LEFT JOIN `course_user` as cu ON cu.`user_id` = u.id AND cu.`relation_type` = 1
LEFT JOIN `courses` AS c On c.id = cu.`course_id`


LEFT JOIN `training_centers` as tc On tc.id = c.`training_center_id`
LEFT JOIN `training_providers` AS tl ON tl.id = tc.`training_provider_id`
/*** Training location **/
LEFT JOIN `provinces` as pt On pt.`province_code` = tc.`province`
LEFT JOIN `districts` as dt on dt.`district_code` = tc.`district`
LEFT JOIN `course_attendances` as ca ON ca.`course_id` = c.`id`
LEFT JOIN `student_attendances` as sa ON sa.`course_attendance_id` = ca.`id`

WHERE c.id IS NOT NULL AND sa.`participant_id` = u.id
GROUP BY sa.`participant_id`,ca.date order by u.id,ca.date

我想用mysql获取上述查询的列名。当然，使用php我们可以做到这一点，但我的问题是，如何使用mysql查询来做到这一点？有可能吗？

Answer 1

MySQL仅仅是一个数据库系统。你告诉它要选择什么，它就会这样做。在您的示例中，告诉它选择courses.id并将其命名为course_id，依此类推。列名在结果中是隐式的。它的工作原理是这样的:您的应用程序将查询发送到MySQL；MySQL对其进行检查，并告诉您是否可以。您的应用程序要求提供列；MySQL会告诉您列的名称和类型。您的应用程序请求行；MySQL将其发送。

通常，你使用的应用程序会自动完成所有这些操作，比如phpMyAdmin。而且，当您自己编写这样的应用程序时，语言通常对您隐藏了所有这些(比如Java framework或.NET)。当然，您也可以明确地询问列名和类型，例如在PHP中：

mysqli_fetch_field_direct($result, $column_index)

通过简单地搜索"MySQL“++”列名“，您可能会找到很多关于如何做到这一点的信息。