Re: What is difference between concatenate & join?
That's not actually accurate. CONCATENATE does create the missing fields from one table into another and adds all the rows, but these are empty or null of they don't have a corresponding field in the concatenated table.
Think of CONCATENATE like an append instruction which add rows no matter the relation the two tables have (as opposed to JOIN, where there must be some type of relation between the tables).
You could indeed concatenate whatever table in the data model to any other table and the result would be a bigger table with as many columns as those in both tables and as many rows as those in each table.