Question

A primary key constraint must ________.

1) reference one or more columns in a single table
2) be defined for every database table
3) be implemented using an index
4) guarantee that no two rows in a table have duplicate primary key values

Answer 1

A primary key constraint must reference one or more columns in a single table and ensure that no two rows have duplicate primary key values. It is often implemented using an index but is not a strict requirement, and while best practice suggests every table should have one, it's not always the case.Option 1 & 4 are the correct answers.

Step-by-step explanation:

The question pertains to the properties that a primary key constraint must ensure in a database system. Here are the accurate statements about a primary key:

1. Reference one or more columns in a single table
2. Guarantee that no two rows in a table have duplicate primary key values

While it's common that a primary key is implemented using an index for performance reasons, it is not a strict requirement of the constraint itself. Also, although it's a best practice to have a primary key for every table to ensure the integrity of the data, there are some rare cases where a table might not have a primary key defined, particularly in the case of temporary tables, staging tables, or when the table is designed to allow duplicate rows.

The properties of a primary key constraint in a database system include referencing one or more columns in a single table and ensuring that no two rows within that table share duplicate primary key values. While indexing is a common practice for performance optimization, it is not a strict requirement of the primary key constraint itself. Although best practices dictate having a primary key for data integrity, exceptional cases exist, such as temporary or staging tables, where a primary key might be omitted. These considerations highlight the flexibility of primary key implementation in specific scenarios based on the nature and purpose of the table.