Help with Mysql Query - Subindex_string + group_concat

Code:

$MyModel->select(SUBSTRING_INDEX(GROUP_CONCAT('id separator ',''), ',', 5))
                    ->orderBy('date', 'DESC')
                    ->groupBy('GROUP')
                    ->limit(2)
                    ->find();

Which still returns the error :  Call to undefined function App\Commands\SUBSTRING_INDEX()

You are using in the select method not a SQL function, but a php function (php thinks so). Therefore, you get an error.
Turn it into a string and you will be happy.