Relational Data Modeling - Primary key

A primary key is a one or more columns that holds the primary key of a row in a table.

A Primary Key identify:

• the lowest level of a table
• the unique identifier of a single row
• doesn't change over time. If the primary key has a chance – however remote – of changing, well, then it is NOT the primary key. This would be like changing your DNA halfway through your life.

A primary key is created with a primary key constraint

A primary key is declared with the creation of a primary key constraint.

Multiple-column primary keys should be avoided as:

• they add complexity in:
  • foreign key constraints .
  • joins
• and may be not supported in all application.

Having a surrogate key as primary key will avoid a Multiple-column primary key.

Surrogate (Sequence, GUID) vs Natural key (Business Key)