Laravel 左连接查询

Question

我使用的是 laravel 5.3，我有一些左连接查询，在 laravel 查询方法中有错误。 这是我的正常查询

 SELECT bran.branchName,sch.schoolName From m_schoolbranch bran
LEFT JOIN m_students stu ON stu.schoolNo=bran.schoolNo AND stu.branchNo=bran.branchNo  
LEFT JOIN m_school sch ON sch.schoolNo=stu.schoolNo where stu.userNo='0000000001';

这是我的新 laravel 查询

DB::table('m_schoolbranch')
            ->join('m_students', 'm_schoolbranch.schoolNo', '=', 'm_students.schoolNo')
            ->join('m_students', 'm_schoolbranch.branchNo', '=', 'm_students.branchNo')
            ->join('m_school', 'm_schoolbranch.schoolNo', '=', 'm_school.schoolNo')
            ->select('m_school.schoolName', 'm_schoolbranch.branchName')
            ->where('m_students.userNo',$userNo)
            ->get();

在这些查询中，我需要匹配表 m_students 中的两列，所以我这样写

->join('m_students', 'm_schoolbranch.branchNo', '=', 'm_students.branchNo')

但我显示错误...

Answer 1

查询中的表需要有唯一的名称，否则数据库无法知道在评估m_schoolbranch.schoolNo 时应该使用哪个m_schoolbranch。

您可以在联接语句中使用唯一的表别名，但我建议在联接中使用多个条件。就像您在原始 SQL 查询中使用的一样。见这里：https://*.com/a/20732468/4437888

Answer 2

DB::table('m_schoolbranch')
            ->join('m_students', function($join)
                {
                    $join->on('m_schoolbranch.schoolNo', '=', 'm_students.schoolNo');
                    $join->on('m_schoolbranch.branchNo', '=', 'm_students.branchNo');
                })
            ->join('m_school', 'm_schoolbranch.schoolNo', '=', 'm_school.schoolNo')
            ->select('m_school.schoolName', 'm_schoolbranch.branchName')
            ->where('m_students.userNo',$userNo)
            ->get();