$scope = function($q){ $q->where('source','like','% P1 %')->orWhere('source','like','% P2 %')->orWhere('source','like','% P3 %'); };
$rows = DB::table('questions')->where($scope)
  ->whereNotNull('explanation')->where('explanation','!=','')
  ->whereNotIn('id', function($q){ $q->select('question_id')->from('solutions'); })
  ->get(['id','explanation']);
$now = now(); $n = 0;
foreach ($rows as $r) {
  DB::table('solutions')->insert([
    'question_id'=>$r->id, 'status_id'=>4, 'source'=>'ai', 'user_id'=>2,
    'solution'=>$r->explanation, 'created_at'=>$now, 'updated_at'=>$now,
  ]);
  $n++;
}
echo "inserted $n solution rows\n";
echo "questions in scope with a linked solution now: ".DB::table('questions')->where($scope)->whereIn('id', function($q){ $q->select('question_id')->from('solutions'); })->count()."\n";