Create hierachy in a dataset

- The structure of an inner join is lackluster.…In my example some customers have multiple…distributors they can pick from…which adds a separate entry for each match.…It would be better to receive the results…in a hierarchical fashion,…where for each customer a list of distributors is returned.…To accomplish that I'll use a GroupJoin.…When executing a GroupJoin the elements…of the left sequence are associated…with one or more matching elements…in the right sequence.…This is also called an"Outer Join"…because the resulting sequence…will include the elements in the left sequence…that are outside of the overlapping areas.…

GroupJoin provides a similar functionality as Join,…but instead of returning a flat structure…it can return a structured result…grouped by each outer element in the resource sequence.…If no matches are found, it will produce…an empty array for that item…as seen here with customer Brock.…To accomplish a GroupJoin I'll add…an into expression to the join clause.…I'll cover the details about the into keyword…