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:

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

Sequence vs business key as primary key

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