In N it is primary key, and X it is foreign key that is why aggregate functions are applied on X’s column because there would be multiple rows for each Key of N in X . i.e., 1 : N ratio between N and X documents.
In N it is primary key, and X it is foreign key that is why aggregate functions are applied on X’s column because there would be multiple rows for each Key of N in X . i.e., 1 : N ratio between N and X documents.