In SQL, relations can contain null values, and comparisons with null values are treated as unknown. Suppose all comparisons with a null value are treated as false. Which of the following pairs is not equivalent?

- $x = 5 \quad not (not (x = 5))$
- $x = 5 \quad x > 4$ and $x < 6,$ where $x$ is an integer
- $x ≠ 5 \quad not (x = 5)$
- none of the above

## 4 Answers

Best answer

Answer is option **C.**

$${\begin{array}{|c|cc|cc|cc|}\hline\\

\textbf{Value at hand}& \textbf{Option A}& & \textbf{Option B}& &\textbf{Option C} \\\hline

6 & \times & \times & \times & \times & \checkmark & \checkmark \\ \hline 5 & \checkmark & \checkmark & \checkmark & \checkmark &\times & \times \\ \hline \text{NULL}& \times & \times & \times & \times &\color{blue} \times & \color{blue}\checkmark \\ \hline

\end{array}}$$