GATE Overflow Test Series | Mixed Subjects | Test 3 | Question: 24

Question

Given the Sailors table
$${\textbf{Sailors}}$$

$${\begin{array}{|c|c|c|c|}
\hline
\textbf{Sid} & \textbf{Sname} & \textbf{Rating} & \textbf{Age}
\\\hline
1 & \text{Peter} & 10 & 23
\\\hline
2 & \text{Alex} & 9 & 24
\\\hline
3 & \text{Alex} & 9 & 25
\\\hline
4 & \text{Michael} & 9 & 24
\\\hline
\end{array}}$$
What does the $\Pi_{\text{Age}}\left[\sigma_{\text{Rating = 9}}[\text{Sailors}]\right]$ give?

• A. $\begin{array}{|c|c|}
  \hline
  \textbf{Age}
  \\\hline
  24
  \\\hline
  25
  \\\hline
  24
  \\\hline
  \end{array}$
• B. $\begin{array}{|c|c|}
  \hline
  \textbf{Age}
  \\\hline
  23
  \\\hline
  24
  \\\hline
  25
  \\\hline
  \end{array}$
• C. $\begin{array}{|c|c|}
  \hline
  \textbf{Age}
  \\\hline
  23
  \\\hline
  24
  \\\hline
  \end{array}$
• D. $\begin{array}{|c|c|}
  \hline
  \textbf{Age}
  \\\hline
  24
  \\\hline
  25
  \\\hline
  \end{array}$

Answer 1

The correct answer is D. Projection operation removes duplicates unlike select in SQL.