How can access be configured with two primary keys?

In a relational database, each table can only have one primary key, which is used to uniquely identify each row of data in the table. If multiple unique identifiers are needed, consider using a composite primary key, which is made up of multiple fields and can uniquely identify a row of data.

To set a composite key, you can either use multiple fields as the primary key when creating the table, or modify the table structure to add a composite key.

Example 1: Setting composite primary keys when creating a table.

CREATE TABLE your_table (
  id INT,
  name VARCHAR(255),
  PRIMARY KEY (id, name)
);

Example 2: Adding a composite primary key by modifying the table structure.

ALTER TABLE your_table
ADD PRIMARY KEY (id, name);

In the example above, we created a table named your_table with two fields, id and name. By setting up these two fields as primary keys, we achieved a composite primary key. This indicates that the combination of id and name must be unique within the table.

It is important to note that composite keys may increase the complexity of queries and performance overhead. Therefore, careful consideration and evaluation of the data model’s requirements and frequency of query operations are needed before setting a composite key.