The primary key data type must be numeric, integer, or fixed-width short characters. Uniqueness is important. A primary key must have unique values. This means that columns in other rows in the table do not contain the same value. These columns are preferable for a primary key. While assigning primary key to the column we need to make sure to keep both data integrity and query performance in mind. A primary key not only guarantees the uniqueness of each row across a table, but it also helps in querying data and maintaining the database.