Соединение Laravel и левое соединение вместе в запросе

Используя построитель запросов, вы можете написать свой запрос как

DB::table('answers as a')
    ->join('questions as q', 'q.id', '=', 'a.question_id')
    ->join('users as u', 'u.id', '=', 'a.user_id')
    ->leftJoin('upvote_answers as ua', function ($join) {
        $join->on('ua.answer_id', '=', 'a.id')
             ->where('ua.user_id', '=', 2);
    })
    ->where('q.question_active', '=', 1)
    ->where('a.answer_active', '=', 1)
    ->select(DB::raw('a.answer_content as answer_content,a.id as answer_id,a.created_at as created_at,a.created_at as answer_upvote,a.created_at as answer_downvote,q.id as question_id, q.question_title as question_title, q.question_slug as question_slug, u.id as user_id, u.name as user_name, u.user_slug as user_slug,ua.upvote as upvote'))
    ->get();

Используйте пункт «Присоединиться»

https://laravel.com/docs/master/queries#joins

Простой пример

$users = DB::table('users')
            ->join('contacts', 'users.id', '=', 'contacts.user_id')
            ->join('orders', 'users.id', '=', 'orders.user_id')
            ->select('users.*', 'contacts.phone', 'orders.price')
            ->where('users.id', '=', 100)
            ->get();

Также вы можете использовать предложение Left Join.

Обновление:

$yourQuery = \DB::table('answers')
    ->join('questions', 'questions.id', '=', 'answers.question_id')
    ->join('users', 'users.id', '=', 'answers.user_id')
    ->leftJoin('upvote_answers', 'upvote_answers.answer_id', '=', 'answers.id')
    ->where('questions.question_active', '=', '1')
    ->where('answers.answer_active', '=', '1')
    ->selectRaw('answers.answer_content as answer_content,
                  answers.id as answer_id,
                  answers.created_at as created_at,
                  answers.created_at as answer_upvote,
                  answers.created_at as answer_downvote,
                  questions.id as question_id, 
                  questions.question_title as question_title, 
                  questions.question_slug as question_slug, 
                  users.id as user_id, 
                  users.name as user_name, 
                  users.user_slug as user_slug,
                  upvote_answers.upvote as upvote');

echo $yourQuery->toSql(); //generated sql query as string
//$yourQuery->get(); //for get data from db

Результат:

выберите answer_content как answer_content,answers.id как answer_id,answers.created_at как created_at,answers.created_at как answer_upvote,answers.created_at как answer_downvote, questions.id как question_id, questions.question_title как question_title, questions.question_slug как question_slug,users .id как user_id, users.name как user_name, users.user_slug как user_slug, upvote_answers.upvote как голосование из ответов на вопросы о внутреннем соединении по вопросам. upvote_answers.answer_id = answer.id, где questions.question_active = ? и ответы.answer_active = ?

Если вам нужно upvote_answers.user_id = '2' в левом соединении, необходимо использовать предварительное левое соединение:

->leftJoin('upvote_answers', function($advancedLeftJoin){
    $advancedLeftJoin->on('users.id', '=', 'contacts.user_id')
        ->where('upvote_answers.user_id', '=', 2);
})

Наконец, ответ для вашего примера:

$yourQuery = \DB::table('answers')
    ->join('questions', 'questions.id', '=', 'answers.question_id')
    ->join('users', 'users.id', '=', 'answers.user_id')
    ->leftJoin('upvote_answers', function($advancedLeftJoin){
        $advancedLeftJoin->on('users.id', '=', 'contacts.user_id')
            ->where('upvote_answers.user_id', '=', 2);
    })
    ->where('questions.question_active', '=', '1')
    ->where('answers.answer_active', '=', '1')
    ->selectRaw('answers.answer_content as answer_content,
                  answers.id as answer_id,
                  answers.created_at as created_at,
                  answers.created_at as answer_upvote,
                  answers.created_at as answer_downvote,
                  questions.id as question_id, 
                  questions.question_title as question_title, 
                  questions.question_slug as question_slug, 
                  users.id as user_id, 
                  users.name as user_name, 
                  users.user_slug as user_slug,
                  upvote_answers.upvote as upvote');

echo $yourQuery->toSql(); //generated sql query as string
//dd($yourQuery->get()); //result as collection

Результат:

выберите answer_content как answer_content,answers.id как answer_id,answers.created_at как created_at,answers.created_at как answer_upvote,answers.created_at как answer_downvote, questions.id как question_id, questions.question_title как question_title, questions.question_slug как question_slug,users .id как user_id, users.name как user_name, users.user_slug как user_slug, upvote_answers.upvote как голосование из ответов на вопросы о внутреннем соединении по вопросам. users.id = contact.user_id и upvote_answers.user_id = ? где questions.question_active = ? и ответы.answer_active = ?

? значение привязывается после использования ->get()