如何过滤groupBy（）只显示Laravel中每个组中的最高值？

My aim of this data is to get the child latest class.

My table:

| id | child_id | class_id   |
|----|----------|------------|
| 1  | 1        | 15         |
| 2  | 2        | 18         |
| 3  | 1        | 19         |
| 4  | 1        | 17         |

Expected result:

| id | child_id | class_id   |
|----|----------|------------|
| 2  | 2        | 18         |
| 4  | 1        | 17         |

Actual result:

| id | child_id | class_id   |
|----|----------|------------|
| 1  | 1        | 15         |
| 2  | 2        | 18         |

I am currently using Enrolment::orderBy('id', 'desc')->groupBy('child_id')->get(); . However it's not working correctly.

Try this code.

select * from  table1
where id in (
    select 
        Max(id) as t.id
    from table1 as t
    GROUP BY t.child_id ORDER BY t.id desc
)

This way, it could solve your problem:

SELECT * FROM `table_name` WHERE `id` IN (SELECT MAX(`id`) FROM `table_name` GROUP BY `child_id`) 

You can use MAX to show highest value

 $response= Enrolment::groupBy('child_id')->get(['child_id', DB::raw('MAX(class_id) as class_ids')]);

and print result as

echo "<pre>";
print_r($response->toArray());

output will be

Array
(
    [0] => Array
        (
            [child_id] => 1
            [class_ids] => 19
        )

    [1] => Array
        (
            [child_id] => 2
            [class_ids] => 18
        )

)

Don't forget to import use DB; in controller