在laravel中获取多对多关系计数的最佳有效方法是什么？

我有多对多关系的

学生

和

主题

表（透视表是学生_主题）

学生模型

public function subjects()
{
    return $this->belongsToMany(Subject::class, 'student_subject');
}

主题模式

public function students()
{
    return $this->belongsToMany(Student::class, 'student_subject');
}

在这里，我要特别的学生科目。我试过下面的方法，效果很好，但我想用最有效的方法

一,

我通过laravel调试程序检查了SQL查询，如下所示

select * from `students` where `students`.`id` = '10' limit 1

select count(*) as aggregate from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `student_subject`.`student_id` = 10 and `subjects`.`deleted_at` is null

select `students`.*, (select count(*) from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `students`.`id` = `student_subject`.`student_id` and `subjects`.`deleted_at` is null) as `subjects_count` from `students` where `students`.`id` = '10' limit 1

select * from `students` where `students`.`id` = '10' limit 1

select `id`, (select count(*) from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `students`.`id` = `student_subject`.`student_id` and `subjects`.`deleted_at` is null) as `subjects_count` from `students` where `students`.`id` in (10)

select * from `students` where `students`.`id` = '10' limit 1

select count(*) as aggregate from `student_subject` where `student_id` = 10

我通过laravel调试程序检查了SQL查询，如下所示

select * from `students` where `students`.`id` = '10' limit 1

select count(*) as aggregate from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `student_subject`.`student_id` = 10 and `subjects`.`deleted_at` is null

select `students`.*, (select count(*) from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `students`.`id` = `student_subject`.`student_id` and `subjects`.`deleted_at` is null) as `subjects_count` from `students` where `students`.`id` = '10' limit 1

select * from `students` where `students`.`id` = '10' limit 1

select `id`, (select count(*) from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `students`.`id` = `student_subject`.`student_id` and `subjects`.`deleted_at` is null) as `subjects_count` from `students` where `students`.`id` in (10)

select * from `students` where `students`.`id` = '10' limit 1

select count(*) as aggregate from `student_subject` where `student_id` = 10

我通过laravel调试程序检查了SQL查询，如下所示

select * from `students` where `students`.`id` = '10' limit 1

select count(*) as aggregate from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `student_subject`.`student_id` = 10 and `subjects`.`deleted_at` is null

select `students`.*, (select count(*) from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `students`.`id` = `student_subject`.`student_id` and `subjects`.`deleted_at` is null) as `subjects_count` from `students` where `students`.`id` = '10' limit 1

select * from `students` where `students`.`id` = '10' limit 1

select `id`, (select count(*) from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `students`.`id` = `student_subject`.`student_id` and `subjects`.`deleted_at` is null) as `subjects_count` from `students` where `students`.`id` in (10)

select * from `students` where `students`.`id` = '10' limit 1

select count(*) as aggregate from `student_subject` where `student_id` = 10

我通过laravel调试程序检查了SQL查询，如下所示

select * from `students` where `students`.`id` = '10' limit 1

select count(*) as aggregate from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `student_subject`.`student_id` = 10 and `subjects`.`deleted_at` is null

select `students`.*, (select count(*) from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `students`.`id` = `student_subject`.`student_id` and `subjects`.`deleted_at` is null) as `subjects_count` from `students` where `students`.`id` = '10' limit 1

select * from `students` where `students`.`id` = '10' limit 1

select `id`, (select count(*) from `subjects` inner join `student_subject` on `subjects`.`id` = `student_subject`.`subject_id` where `students`.`id` = `student_subject`.`student_id` and `subjects`.`deleted_at` is null) as `subjects_count` from `students` where `students`.`id` in (10)

select * from `students` where `students`.`id` = '10' limit 1

select count(*) as aggregate from `student_subject` where `student_id` = 10

根据以上方法，哪一个是最好的，为什么？或者，如果有任何不同的最佳方法也存在？

执行

关系（）->count（）

可能更快

---

但是，如果您只需要计数，

withCount（）

在内存消耗方面应该更好。

谢谢您的时间，我需要一种有正确理由的最有效的方法。你的回答没有任何完美的理由。没问题！看看这是否有帮助：根据上面的链接，

withCount

比

with

的内存效率更高。那么

loadCount

？那将是急切加载与惰性加载。由于您没有根据某些动态条件加载计数，因此无需使用

loadCount（）

运行第二个查询。因此，在您的上下文中，

withCount（）

也是一个更好的选择。我同意您的观点。但请检查我的SQL查询中的每一点。因此，我认为第四个是最好的（花更少的时间，因为它没有检查与受试者的任何关系）