mysql - Laravel Eloquent 组按最新记录

Question

我正在尝试获取一张 table 上单个客户的最新记录。示例:

ID    Customer    City    Amount
1     Cust001     City1   2
2     Cust001     City2   3
3     Cust001     City1   1
4     Cust001     City2   1
5     Cust001     City2   3
6     Cust001     City3   1
7     Cust001     City3   1
8     Cust002     City1   2
9     Cust002     City1   1
10    Cust002     City2   3
11    Cust002     City1   2
12    Cust002     City2   1
13    Cust002     City3   2
14    Cust002     City3   3
15    Cust003     City1   1
16    Cust003     City2   3
17    Cust003     City3   2

请注意该表还有 created_at 和 updated_at 字段。为简单起见，我省略了这些字段。

最后，我希望我的查询返回 Cust001:

ID    Customer    City    Amount
3     Cust001     City1   1
5     Cust001     City2   3
7     Cust001     City3   1

对于 Cust002:

ID    Customer    City    Amount
11    Cust002     City1   2
12    Cust002     City2   1
14    Cust002     City3   3

我试过:

Table::where('Customer', 'Cust001')
    ->latest()
    ->groupBy('City')
    ->get()

还有

Table::select(DB::raw('t.*'))->from(DB::raw('(select * from table where Customer = \'Cust001\' order by created_at DESC) t'))
    ->groupBy('t.City')->get();

但它不断返回每个组中最旧的记录(我想要最新的)。

我怎样才能做到这一点？如果对你们来说更容易，你们可以在这里编写 SQL 查询，我会找到一种方法将它“翻译”成 Laravel 语法。

Answer 1

要根据 created_at 获取每个城市的每个客户的最新记录，您可以使用自连接

DB::table('yourTable as t')
  ->select('t.*')
  ->leftJoin('yourTable as t1', function ($join) {
        $join->on('t.Customer','=','t1.Customer')
             ->where('t.City', '=', 't1.City')
             ->whereRaw(DB::raw('t.created_at < t1.created_at'));
   })
  ->whereNull('t1.id')
  ->get();

在普通的 SQL 中，它类似于

select t.*
from yourTable t
left join yourTable t1
on t.Customer = t1.Customer
and t.City = t1.City
and t.created_at < t1.created_at
where t1.id is null

Demo

另一种 self 内连接的方法是

select t.*
from yourTable t
join (
    select  Customer,City,max(ID) ID
    from yourTable
    group by Customer,City
) t1
on t.Customer = t1.Customer
and t.City = t1.City
and t.ID = t1.ID

Demo