使用数据透视表查询的动态列

Question

我有这个出勤表

---------------------------------------------------------------------------
attendance_id | stud_id      | week       | sy        |sem         |present
---------------------------------------------------------------------------
1             | 1            | 02/18/2012 | 2010-2011 |1st semester|1
2             | 2            | 02/18/2012 | 2010-2011 |1st semester|1
3             | 3            | 02/18/2012 | 2010-2011 |1st semester|1
4             | 1            | 02/25/2012 | 2010-2011 |1st semester|1
5             | 2            | 02/25/2012 | 2010-2011 |1st semester|1
6             | 1            | 03/03/2012 | 2010-2011 |1st semester|1
7             | 2            | 03/03/2012 | 2010-2011 |1st semester|1
8             | 3            | 03/03/2012 | 2010-2011 |1st semester|1

我的查询是

Select cadet_record.fname,cadet_record.lname,cadet_record.mname, student_id,

MAX(case WHEN week = '02/18/2012' then present end) as 'week1',
MAX(case WHEN week = '02/25/2012' then present end) as 'week2'
From attendance
LEFT JOIN cadet_record ON cadet_record.stud_no = attendance.student_id WHERE section = '$section' AND schoolyear = '$year' AND component = '$component' AND semester = '$semester'
GROUP BY student_id

如何在不插入日期的情况下动态调用一周 例如02/28 / 2012,02 / 29/2012等等。 有任何想法吗？ =（

Answer 1

据我所知，您无法动态地将列添加到SELECT语句中。您要求的是一种呈现数据的方式，这不是MySQL所关心的。你应该在前端处理它。

但是，您可以通过在模型中创建查询并动态添加这些新列来作弊，方法是在查询字符串中动态插入更多MAX(case...。不过，这不是一个好的解决方案。

修改

  

我使用php，我该怎么做？

所以，我想你在谈论丑陋的解决方案。好吧，基本上你应该动态创建你的查询字符串（伪代码）：

$initialDay = 02/28/2012;
$lastDay = 03/28/2012;
$dayNumber = 1;
$sql = 'Select cadet_record.fname,cadet_record.lname,cadet_record.mname, student_id';
while ($initialDay <= $lastDay) {
    $sql .= ', MAX(case WHEN week = $initialDay then present end) as day' . $dayNumber;
    $initialDay = $initialDay + 1 day;
    $dayNumber++;
}
$sql .= ' From attendance blah blah...';

然后，对于2012年2月18日至2012年1月18日的日期，您的查询应如下所示：

Select cadet_record.fname,cadet_record.lname,cadet_record.mname, student_id,
,MAX(case WHEN week = '02/18/2012' then present end) as day1
,MAX(case WHEN week = '02/19/2012' then present end) as day2
From attendance
LEFT JOIN cadet_record ON cadet_record.stud_no = attendance.student_id WHERE section = '$section' AND schoolyear = '$year' AND component = '$component' AND semester = '$semester'

GROUP BY student_id

注意我添加了几天而不是几周，因为您的示例显示了增加的天数，尽管列名是周

Answer 2

如果不旋转表格，您可以通过此查询获得每位学生的每周出勤率：

SELECT 
    cadet_record.fname,
    cadet_record.lname,
    cadet_record.mname, 
    student_id,
    week,
    SUM(present) AS att
FROM attendance
LEFT JOIN cadet_record 
    ON cadet_record.stud_no = attendance.student_id 
WHERE section = '$section' 
    AND schoolyear = '$year' 
    AND component = '$component' 
    AND semester = '$semester'
GROUP BY week, student_id
ORDER BY week, cadet_record.fname, student_id

（编辑抱歉，您应该使用SUM，而不是COUNT。