The Object-Relational Mismatch
Most development takes place in object-oriented programming (OOP) languages, which leads to a common criticism of the SQL data model. If data is stored in relational tables, an awkward translation layer is required between the objects in the application code and the database model of tables, rows, and columns. This is called the object-relational impedance mismatch.
Example: LinkedIn Profile
Suppose a LinkedIn profile has a user_id (primary key). Fields like first_name and last_name appear only once per user, but fields like previous jobs and education history can contain multiple entries.
Traditionally, the most common approach was to create separate tables for jobs and education and link them with the main user table using foreign keys.
