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+Q1:Rank Scores
+--Using window functions
+select score, 
+	dense_rank() over (order by score desc) as 'rnk' 
+from scores 
+order by rnk;
+
+--Without using window functions
+select t.score, 
+		(select count(distinct s.score) 
+		from scores s 
+		where s.score>=t.score) as 'rnk'
+from scores t 
+order by rnk;
+
+Q2:Exchange Seats
+SELECT 
+    CASE 
+        WHEN mod(id 2) !=0 AND id != cnts THEN id + 1
+		WHEN  mod(id 2) != 0 AND id = cnts THEN id
+        ELSE id - 1
+	END
+    AS id,
+    student
+FROM Seat, (select count(*) as cnts from seat) as Seat_Counts
+ORDER BY id;
+
+Q3:TREE NODE
+select distinct t1.id,
+		case
+			when t1.p_id is null then 'root'
+			when t2.id is null then  'leaf'
+			else 'inner'
+		end as type
+from tree t1 
+left join tree t2
+on t1.id=t2.p_id;
+
+Q4:DEPARTMENT TOP3 SALARIES
+# Write your MySQL query statement below
+SELECT Department, Employee, Salary
+FROM (
+    SELECT d.name AS Department, 
+           e.name AS Employee, 
+           e.salary,
+           DENSE_RANK() OVER (PARTITION BY e.departmentId ORDER BY e.salary DESC) AS dr
+    FROM Employee e
+    LEFT JOIN Department d ON e.departmentId = d.id
+) ranked
+WHERE dr <= 3
+ORDER BY Department, Salary DESC, Employee;