RDBMS Data Modeling - Primary key

A Primary Key identify:

• the lowest level of an entity
• the unique identifier of a single instance
• 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 you changing your DNA halfway through your life.

See also: Data Modeling - Identifier - (Id|Primary|Natural|Surrogate|Business) key

Sequence as primary key

• You can't search on the business key in an external table.
• You need to do an extra action to get the primary key (join in SQL or show the information on the screen)

• Gain on IO in the internal table but also in the external table
• If the grain of a (external|dimension) table changes, you don't need to add a column in the fact table