Question

有没有一种雄辩的方法可以从关系表中获得平均值？我这里有 2 张桌子。

我可以使用 withAvg 获得所有考试的平均值，但我还想获得每次考试的平均值（参见预期结果）。有人可以给一个想法如何做到这一点？谢谢

型号：

Student (students)
- id
- name

Exam (exams)
- id
- title
- is_correct
- student_id

StudentExam (studentExams)
- id
- section

我已经尝试过这个并且它工作正常。

StudentExam::whereSection(1)
 ->with('exams')
 ->withAvg('exams AS total_avg_exams', 'is_correct);
 ->first();

结果为：

{
    section: 1,
    total_avg_exams: 0.63,
    exams: [{},{}],
}

预期结果是：

{
    section: 1,
    total_avg_exams: 0.63,
    exams: [
        {
            avg_exams: 0.83,
            ...
        },
        {
            avg_exams: 0.63,
            ...
        }
    ]
}

Answer 1

您需要在 with 语句中对考试进行分组。我假设所有相关的考试都具有相同的标题，所以应该是这样的。


use Illuminate\Support\Facades\DB;

StudentExam::whereSection(1)
 ->with(['exams' => function($query){
//You need the title for grouping
//You will need the student id for the eager loading so relation works
//is_correct is needed for the query
return $query->select(
 'title', 
 'student_id', 
 'is_correct', 
 DB::raw('avg(is_correct) as total_avg_exams'))
->groupBy('title');
}])
 ->withAvg('exams AS total_avg_exams', 'is_correct');
 ->first();

如何获得关系表的平均值？拉拉维尔

1 个答案: