Question

我正在使用Laravel的查询构建器执行此查询，并使用左连接，并在列s_nid上链接两个表。在表格中我离开了加入conference_report的行，其中有一行s_nid，我只希望找回最近日期的行。我一直在关注Groupwise Maximum，这里有一些关于SO的例子，对我来说是新的，我认为我需要完成查询，但我不确定如何在桌面上实现它我加入

$data['students'] = DB::table('educational_report')
        ->select('educational_report.s_nid as s_nid'
                ,'educational_report.name as name'
                ,'educational_report.file_no as file_no'
                ,'educational_report.university as university'
                ,'conference_report.conference_end_date as conference_end_date'
                ,'student_status.status as status')
        ->leftJoin('student_status', 'student_status.s_nid', '=', 'educational_report.s_nid')
        ->leftJoin('conference_report', 'conference_report.s_nid', '=', 'educational_report.s_nid')
        ->distinct()
        ->groupBy('s_nid')
        ->paginate(10);

可能有用的链接：

Performing a Groupwise Maximum in Laravel 4

Groupwise maximum

http://dev.mysql.com/doc/refman/5.6/en/example-maximum-column-group-row.html

Answer 1

我认为我没有必要让事情复杂化。我设法使用连接上的嵌套查询来解决这个问题：

$data['students'] = DB::table('educational_report')
        ->select('educational_report.s_nid as s_nid'
                ,'educational_report.name as name'
                ,'educational_report.file_no as file_no'
                ,'educational_report.university as university'
                ,'cr2.conference_end_date as conference_end_date'
                ,'student_status.status as status')
        ->leftJoin('student_status', 'student_status.s_nid', '=', 'educational_report.s_nid')
        ->leftJoin(DB::raw('(select s_nid, MAX(conference_end_date) conference_end_date
                                from conference_report GROUP BY s_nid) as cr2'), function ($join) {
                                    $join->on ( 'cr2.s_nid', '=', 'educational_report.s_nid' );
                    })
        ->paginate(10);

它似乎工作正常，但我热衷于任何可能纠正我正在做的事情或提供更好方法的答案。谢谢:)）

Laravel获得最近加入表的日期

1 个答案: