sum of costs from another table by current ID - laravel

Question

I have 4 tables:
"Cars" table, where every car has an ID.
"Operations" table that holds the operations have been done on a car.
| ID | CarID | Operation | User | JournalID |
| --- | ----- | --------- | ---- | --------- |
"Transactions" table that records the costs of the operations and other daily expenses, where every operation has 2 transactions, one is > 0 and the other is < 0 (for example: +100 and -100):
| ID | Account | JournalID | Amount | Date |
| --- | ------- | --------- | ------ | ---- |
"Journal" table that records the daily finance:
| ID | Amount | Date |
| --- | ------ | ---- |
What I want is knowing the sum of operations costs amount of a specific car, I was looping through all operations of that car and then looping for every journal row to sum, which lead to a bad result of course.
What can I do in that case to get the result as fast as possible?
NOTE: ALL THE NAMES OF THE COLUMNS ARE IN LOWER CASE

Answer 1

You need to join three tables based on the foreign keys like this and with some select and raw query you can get solution to your problem.
DB::table('cars')->join('operations','cars.id','operations.car_id')
->join('journal','journal.id','operations.journal_id')
->select(DB::raw('SUM(amount) as total_cost'),'cars.*')
->groupBy('cars.id')
->get();

Answer 2

I ended up solving it with #Segar's answer modified:
$result = DB::table('cars')
->join('operations','cars.id','operations.car_id')
->join('journal','journal.id','operations.journal')
->join('transactions','transactions.journal','operations.journal')->where('transactions.type', 0)
->select(DB::raw('SUM(amount) as total_cost'),'cars.*')
->groupBy('cars.id')
->get();
print_r($result);
Thanks.