Complex Laravel SQL queries?

Question

MySQL

I'm very bad with joins, so I've been hustling on the spot for more than an hour.
1 - we have an intermediate table, in it user_id | post_id .

DB::table('user_watchlist')
            ->where('user_id', $userID)
            ->where('user_id', $postD)
// тут надо как-то заджойнить таблицу постов и тсортировать весь результат по тайтлу поста
           // ->orderBy('post_title', 'DESC')
            ->get();

How to connect posts table and filter by post_title?
2 - Return posts, in the name of which and the name of which categories (that is, there is a post, it belongs to the category, and the name of the category is in question) contains the search text. The user entered for example "category", it displays posts with the name "category" and posts whose categories have the name "category".

$results = DB::table('categories')
        ->select('categories.*')
        ->join('posts', 'posts.categories_id', '=', 'categories.id')
        ->where('posts.title', 'like', '%' . $searchText . '%')
        ->orWhere('categories.title', 'like', '%' . $searchText . '%')
        //->orderBy( 'DESC') // и как тут отсортировать?
        ->get();
// вернет только посты

It will return only the table that has been joined.

$query = DB::table('posts')->join('some_pivot_table', 'posts.id', '=', 'some_pivot_table.post_id')->get()

I'm sitting practicing the Laravel 5.4 QueryBuilder manual, a lot is missing here, as if torn out in pieces, nothing is clear. I don't understand how it works.

Answer 1

Create models with the desired relationships. Then
1)
2)

Post::query()->where('title', 'like', "%{$searchText}%")
  ->orWhereHas('category', function (Builder $query) use ($searchText) {
    $query->where('title', 'like', "%{$searchText}%"); // Это относится к таблице с категориями 
  })
  ->orderBy('title', 'DESC')
  ->get();

Without models if
1)

DB::table('posts')
    ->select('posts.*')
    ->where('user_id', $userID)
    ->join('user_watchlist', 'user_watchlist.post_id', '=', 'posts.id')
    ->orderBy('posts.title', 'DESC')
    ->get();

2)

DB::table('posts')
    ->select('posts.*')
    ->join('categories', 'posts.categories_id', '=', 'categories.id')
    ->where('posts.title', 'like', '%' . $searchText . '%')
    ->orWhere('categories.title', 'like', '%' . $searchText . '%')
    ->orderBy('posts.title', 'DESC')
    ->get();