Relational Database Management Systems (RDBMS)
Data is organized in tables defined by the relations of the data into organized tables.
Tables can have Primary AND/OR Unique keys.
They can also have Foreign Keys (FK)
Generally, each table/relation represents one "entity type" (such as customer or product - names of the tables).
Tables have columns and rows.
Every row represents an instance of related column values.
Primary Key represents NOT nullable values of a table and remain unique.
Unique Key also represents in a database relational modeling and implementation, a unique key (also known as a candidate key or just a key) is a set of attributes (columns) within a relational database table (also called a relation)
Foreign Key (FK) is a key to link 2 or more tables. FK is column/s in a table that refers to a PK in another table.