Is it possible to set NULL value for a primary key in a database?

In most relational databases, the primary key (PRIMARY KEY) cannot accept a NULL value. This is because the primary key serves as a unique identifier for a record, and its value must be unique and present.

If you try to insert NULL into a field declared as PRIMARY KEY, the database will return an error.

If a field is needed that can be empty but still unique, a unique index (UNIQUE) can be used without the NOT NULL constraint, but this will not be a primary key.

Thus, setting a NULL value for a primary key is impossible according to relational database standards.