mysql - Order by from multiple tables in Laravel - mysql

Question

I have 3 tables topic1, topic2, topic3. I split into 3 tables because of huge difference in attributes. all of these table has a common column of created_timestamp
I would like to create a timeline displaying from the latest with the created_timestamp as reference.
I have tried joining the tables and order by greatest (t1.created_timestamp, t2.created_timestamp, t3.created_timestamp) but I can't do this in the query builder of laravel.
Plus when displaying of the attributes, they will be repeated, is there a way to only show topic1 attributes if topic1 is the latest, so on and so forth.
Or is there a better method?
Thank you Jedi masters!
I forgot to mention about a fourth table (follower table) that only shows the created_by of the 3 topic tables.
topic1 {var1, var2, created_timestamp, user_id)
topic2 {var3, var2, var3, created_timestamp, teacher_id)
topic3 {var3, created_timestamp, visitor_id)
follower {follow_id, creator_id}
follow_id = user_id, teacher_id, visitor_id (table joins)
I would need to get only rows that I follow (aka where follower.creator_id = $me)

Answer 1

I think the best way would be to run a query for each table and then combine the results.
$a = DB::table('topic1')->join('follower', 'folower.follow_id', '=', 'topic1.user_id')->where('folower.follower_id', $followed)->get();
$b = DB::table('topic2')->join('follower', 'folower.follow_id', '=', 'topic2.teacher_id')->where('folower.follower_id', $followed)->get();
$c = DB::table('topic3')->join('follower', 'folower.follow_id', '=', 'topic3.visitor_id')->where('folower.follower_id', $followed)->get();
$results = new Illuminate\Database\Eloquent\Collection;
$results = $results->merge($a)->merge($b)->merge($c)->sortBy('created_timestamp');