Getting the unique year value in Laravel - laravel

Question

I just wanted to extract unique year value from this date type column. But I always get this error "You might need to add explicit type casts".
If there are 2020-06-23, 2020-07-01, 2019-01-02, 2019-02-05 dates, my desired output is to return the unique year values. So the output should be 2020 and 2019 only.Please help. Thank you.
Here is my code:
$year= DB::table('loans')
->select('date_release', DB::raw('YEAR(date_release) as year'))
->groupBy('year')
->get();

Answer 1

The query could be (returns all when there are different dates from different years);
SELECT EXTRACT(YEAR FROM loans.date_release) AS year FROM loans group by year;
The query builder will be
return DB::table('loans')
->select([DB::raw('EXTRACT(YEAR FROM loans.date_release) as year')])
->groupBy('year')
->pluck('year');
it prints following for multiple years
[2018, 2019, 2020]

Answer 2

I think that there are only 2 ways to get what you want
first you need add another column with name year and store data only year and your query will be like this
return DB::table('loans')
->select('year')->distinct('year');
second one is before return you should some algorithm to extract year and return only distinct year it will be like this
$year = DB::table('loans')
->select([DB::raw('YEAR(date_release) as year')])
->groupBy('year')
->value('year');
$distinct_year = array();
foreach($year as $item){
$years = date('Y', strtotime($item->year))
if(!in_array($years, $distinct_year)){
array_push($distinct_year, $years);
}
}
return $distinct_year;