MySQL Database, Query Builder: Join and Union

Laravel Course

Laravel's database query builder provides a convenient, fluent interface to creating and running database queries.
- It uses PDO parameter binding to protect your application against SQL injection. There is no need to clean strings passed as bindings.

Joins

To perform a basic "inner join", you may use the join() method on a query builder instance.
The first argument is the name of the table you need to join to; the remaining arguments specify the relation of the columns for the join.
- You can join to multiple tables in a single query:

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

- To perform a "left join" query, use the leftJoin() method, in the same way as the join() method.

$users = DB::table('users')
 ->leftJoin('posts', 'users.id', '=', 'posts.user_id')
->get();

Unions

To "union" two queries together, create an initial query and use the union() method to union it with a second query.

$first = DB::table('users')->whereNull('first_name');

$users = DB::table('users')->whereNull('last_name')
->union($first)->get();

- Documentation: Laravel - Database: Query Builder

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