What is a primary key constraint?

A primary key provides a unique identifier for every row in a global or central table; where a key is defined by a combination of one or more columns in the table.

A primary key constraint enforces the uniqueness of primary keys in a global or central table, so that any attempt to insert or update rows which would create duplicated primary keys are prevented.

Creating a primary key constraint both defines the primary key and enforces it; and there can only be one primary key constraint defined per table.

You cannot delete rows that are referenced by a foreign key constraint in the same or another table.


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