使用 group by 和 Laravel 获取最新行-数据库问题

Get most recent row with group by and Laravel(使用 group by 和 Laravel 获取最新行)

本文介绍了使用 group by 和 Laravel 获取最新行的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

即使有多个这样的问题，我也无法让我的查询返回具有最近日期的行和 group by.

Even though there are multiple questions like this I can't get my query to return the row with the most recent date with a group by.

我有下表..

| message_id | from | to | created_at | status
----------------------------------------------
|    1       |   1  |  2 | 2017-04-06 |   1
|    2       |   1  |  2 | 2017-04-07 |   0
|    3       |   3  |  4 | 2017-04-06 |   1
|    4       |   3  |  4 | 2017-04-07 |   0
----------------------------------------------

我正在尝试获取最新日期的行.

and I'm tryin to get the rows with most recent date.

| message_id | from | to | created_at | status
----------------------------------------------
|    2       |   1  |  2 | 2017-04-07 |   0
|    4       |   3  |  4 | 2017-04-07 |   0

目前此查询返回最近日期的行.

Currently this query returns the rows with the last recent date.

$messages = Message::where('to', Auth::id())
                    ->groupBy('from')
                    ->orderBy('created_at', 'DESC')
                    ->paginate(10);

推荐答案

问题是结果集会先分组然后有序.您可以使用嵌套选择来获取您想要的内容.

The problem is that the result set will be first grouped then ordered. You can use nested select to get what you want.

SQL 查询:

SELECT t.* FROM (SELECT * FROM messages ORDER BY created_at DESC) t GROUP BY t.from

使用 Laravel:

With Laravel:

$messages = Message::select(DB::raw('t.*'))
            ->from(DB::raw('(SELECT * FROM messages ORDER BY created_at DESC) t'))
            ->groupBy('t.from')
            ->get();

您只需要添加您的 where() 子句.

You just need to add your where() clauses.

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