NIELIT 2021 Dec Scientist A - Section B: 83

Question

Consider the following statements :

1. The primary key of a relation cannot contain null values.
2. Unique Key can have null values.

Which among the following is true ?

• A. Both $\text{I}$ and $\text{II}$ are true
• B. Both $\text{I}$ and $\text{II}$ are false
• C. Only $\text{I}$ is true
• D. Only $\text{II}$ is true

Answer 1

A primary key column cannot contain NULL values, whereas a unique key can have NULL values, but only one NULL is allowed in a table. A primary key should be unique, but a unique key cannot necessarily be the primary key. The primary key by default is a clustered index where data is physically organized in the sequential index.

Reference: Difference between Primary Key and Unique key - javatpoint