Consider the following relation.
$$\textbf{Emp}$$$$\begin{array}{|c|c|c|c|c|c|c|}
\hline
\underline{\textbf{EmpId}} & \textbf{DeptNo} & \textbf{EmpName} & \textbf{Salary} \\
\hline
1 & 5 & \text{Alex}&10,000 \\
\hline
2 & 2 & \text{Steve}&20,000 \\
\hline
3 & 1 & \text{Bob} &15,000 \\
\hline
4 & 2 & \text{Smith}&18,000 \\
\hline
5 & 4 & \text{Rakul}&24,000 \\
\hline
6 & 3 & \text{Rhea}&17,000 \\
\hline
\end{array}$$
$$\textbf{Dept}$$$$\begin{array}{|c|c|c|c|c|c|c|}
\hline
\underline{\textbf{DeptId}} & \textbf{DeptName} \\
\hline
1 & \text{CSE} \\
\hline
2 & \text{ECE} \\
\hline
3 & \text{ECE} \\
\hline
4 & \text{IT} \\
\hline
5 & \text{ME} \\
\hline
\end{array}$$
Here, Emp(DeptNo) is the foreign key referring to Dept(DeptId).
The number of tuples returned by the following SQL query is _____
SELECT max(Salary) FROM Emp, Dept
WHERE Emp.DeptNo = Dept.DeptId group by Dept.DeptId;