title: Composite key in associative tables
body: <p>I know that for associative entities, the unique identifiers from the neighboring entities must included within the associative entity to have the PK-FK constraint. And we create the constraint between the PK-FK keys with their respective neighbors in the SQL DDL commands. </p>
  
  <p>However, when creating the SQL DDL commands, do we also have to create a composite key for that associative table as well (in addition to the PK-FK key constraints)? Help is much appreciated, thanks. </p>