About
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 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
Management
Declaration
A primary key is declared with the creation of a primary key constraint.
Multiple-column
Multiple-column primary keys should be avoided as:
- they add complexity in:
- and may be not supported in all application.
Having a surrogate key as primary key will avoid a Multiple-column primary key.