laravel：错误：使用连接，原始和查询答案

【问题标题】：laravel: error: using join, raw and having in querylaravel：错误：使用连接，原始和查询
【发布时间】：2020-03-21 14:40:45
【问题描述】：

我使用 laravel 框架。我写了这个查询，但它显示了一个错误：

错误：

SQLSTATE[42S22]: Column not found: 1054 Unknown column 'schools.grade' in 'field list' (SQL: select `students`.`name`, `students`.`lastname`, students.id, max(`schools.grade`) as `grade` from `students` inner join `schools` on `schools`.`id` = `students`.`id` group by `schools`.`id` having `grade` = 6)

我的代码：

$stu = students::join('schools', 'schools.id',"=", 'students.id')
            ->select('students.name','students.lastname',DB::raw('students.id, max(`schools.grade`) as `grade`'))
            ->groupBy('schools.id')
            ->having('grade','=',$grade)
            ->get();
        dd($stu);

怎么了？谢谢

【问题讨论】：

显而易见的问题：schools.grade 存在吗？听起来grade 属于students。
是的，schools.grade 绝对存在于表中。

标签： mysql laravel laravel-5

【解决方案1】：

我检查了这两个查询作为测试，它们都单独工作。但可能主查询（我首先提到的）不起作用。

DB::table('schools')
         ->select(DB::raw('id, max(`grade`) as `grade`'))
          ->groupBy('id')
          ->having('grade','=',$grade)
         ->get();

和：

$stu = students::join('schools', 'schools.id',"=", 'students.id')
         ->select('students.name','students.lastname','students.id','schools.grade')
           ->where('schools.grade','=',$grade)  
           ->get();

【讨论】：

【解决方案2】：

首先要验证grade 在schools 表中是否有列，因为很可能这就是这里的问题。

如果您认为它确实存在，请尝试在having 条件下使用表名：

$stu = students::join('schools', 'schools.id',"=", 'students.id')
            ->select('students.name','students.lastname',DB::raw('students.id, max(`schools.grade`) as `grade`'))
            ->groupBy('schools.id')
            ->having('schools.grade','=',$grade)
            ->get();
dd($stu);

【讨论】：

【解决方案3】：

你写的是这样的......

   $stu = students::join('schools', 'schools.id',"=", 'students.id')
        ->select('students.name','students.lastname',DB::raw('students.id,max(`schools.grade`) as `grade`'))
        ->groupBy('schools.id')
        ->having('schools.grade','=',$grade)->get();
    dd($stu);

【讨论】：

【解决方案4】：

$stu = students::join('schools as s', 's.id',"=", 'students.id')
            ->select('students.name','students.lastname','students.id, 
               DB::raw(max(`s.grade`) as `grade`')) // make sure grade exist in school? if in student then use students.grade in db:Row
            ->groupBy('s.id')
            ->having('grade','=',$grade)
            ->get();

【讨论】：