Add Returning With Sequel as a ruby til

ruby/returning-with-sequel.md

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+# Returning With Sequel
+
+The [`sequel`](https://github.com/jeremyevans/sequel) gem is a database
+toolkit that allows you to interact with most databases. PostgreSQL has
+support for composite primary keys, but `sequel`, which is supposed to return
+the `id` of newly inserted records, isn't sure what to return when faced
+with a composite primary key. You can get around this by telling `sequel`
+exactly what should be returned using the `#returning` method. For instance,
+get it to return just the `id` of the new record:
+
+```ruby
+DB[:floors].returning(:id).insert(hotel_id: 4, id: 1, ...)
+# [{id: 1}]
+```
+
+To get it to return both parts of composite key:
+
+```ruby
+DB[:floors].returning(:id, :hotel_id).insert(hotel_id: 4, id: 1, ...)
+# [{id: 1, hotel_id: 4}]
+```