What is the difference between a primary key and a unique key in Oracle?

```html

Understanding the Difference Between Primary Key and Unique Key in Oracle

When working with database systems like Oracle, it's crucial to grasp the distinctions between a primary key and a unique key to maintain data integrity and enforce constraints effectively.

Primary Key in Oracle

The primary key in Oracle is a column or set of columns that uniquely identifies each record in a table. It ensures that each row in the table has a distinct identity and cannot contain null values.

Unique Key in Oracle

On the other hand, a unique key constraint in Oracle also enforces uniqueness on a column or set of columns but allows null values. This means that while each value in the unique key column(s) must be unique, it does not require the column(s) to be populated with non-null data.

It's important to note that a table can have only one primary key, while multiple unique keys can be defined in a table.

In summary, the primary key ensures both uniqueness and non-null values, while the unique key enforces only uniqueness without the restriction on null values.

```