Laravel eloquent select first row of each group by

Question

I have subjects table and tutorials table in SQLite database. I am trying to select current tutorial. There are my tables

• Subjects table:

  -------------------
  |  id |   name    |
  -------------------
  |  1  | Chemistry |
  |  2  | Physic    |
  -------------------
  

• Tutorials table:

  -----------------------------------------
  | id  |    name   | subj_id | completed |
  -----------------------------------------
  |  1  | chapter 1 |   1     |     1     |
  |  2  | chapter 2 |   1     |     0     |
  |  3  | chapter 3 |   1     |     0     |
  |  4  | chapter 1 |   2     |     1     |
  |  5  | chapter 2 |   2     |     1     |
  |  6  | chapter 3 |   2     |     0     |
  |  7  | chapter 4 |   2     |     0     |
  -----------------------------------------
  

My current eloquent is:

  $query->where('completed', false)->groupBy('subj_id')->get();

And it returns the following:

-----------------------------------------
| id  |    name   | subj_id | completed |
-----------------------------------------
|  3  | chapter 3 |   1     |     0     |
|  7  | chapter 4 |   2     |     0     |
-----------------------------------------

Now I wish to select id 2 and 6.

-----------------------------------------
| id  |    name   | subj_id | completed |
-----------------------------------------
|  2  | chapter 2 |   1     |     0     |
|  6  | chapter 3 |   2     |     0     |
-----------------------------------------

How could I get id 2 and 6 using sqlite?

Answer 1

My problem is solved by @zerofl4g's help.

This eloquent helped by @zerofl4g.

$query->select(DB::raw("SELECT MIN(id), name, subj_id FROM tutorials
 WHERE completed = 0 GROUP BY subj_id"));

It doesn't work for me but help me a lot. I don't know the precise reason why not worked form me but I think I am using it as subquery. So I got duplicate select and from errors. It must surely work for someone who want to use as single query.

My solution is just select columns with DB::raw and ->from('tutorials') is also optional, as it is subquery of a long query

$query->select(DB::raw('MIN(id) as id, name, subj_id'))->from('tutorials')
->where('completed', false)->groupBy('subj_id');

Final eloquent I am using is

$query->select(DB::raw('MIN(id) as id, name, subj_id'))
->where('completed', false)->groupBy('subj_id');`

Hope to be helpful.

Answer 2

If you want to return first row in group by, you can try the code below. I think what you want to get is the latest chapter in the subject that not finish.

$data = Tutorial::where('completed', 0)->get();
$groups = $data->groupBy('subj_id');

$results = [];
foreach($groups as $group) {
    $results[] = head($group);
}
return $results;

1. Get all tutorials row

2. Then, group by subj_id. The data you get is like below

{
    1: [{
        id: "2",
        name: "chapter 2",
        subj_id: "1",
        completed: "0"
    }, {
        id: "3",
        name: "chapter 3",
        subj_id: "1",
        completed: "0"
    }],

    2: [{
        id: "6",
        name: "chapter 3",
        subj_id: "2",
        completed: "0"
    }, {
        id: "7",
        name: "chapter 4",
        subj_id: "2",
        completed: "0"
    }]
}

3. Foreach each group and get the minimum id by using head() helper function in laravel.

Answer 3

Correct query will be like

$query->where('completed', false)->get()->groupBy('subj_id');

get() will be call first before groupBy. I mean once get() make collection you can use all collection method. for more details and know all collection method https://laravel.com/docs/5.8/collections#method-groupby