diff --git a/Problem 1.sql b/Problem 1.sql
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+++ b/Problem 1.sql	
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+# Write your MySQL query statement below
+SELECT score, DENSE_RANK() OVER(ORDER BY score DESC) AS 'rank' FROM Scores
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diff --git a/Problem 2.sql b/Problem 2.sql
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+++ b/Problem 2.sql	
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+# Write your MySQL query statement below
+SELECT (CASE
+    WHEN id%2=1 AND id=(SELECT MAX(id) FROM Seat) THEN id
+    WHEN id%2=1 THEN id+1
+    ELSE id-1
+    END
+)AS id, student FROM Seat ORDER BY id
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diff --git a/Problem 3.sql b/Problem 3.sql
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+++ b/Problem 3.sql	
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+SELECT id, (
+    CASE
+    WHEN ISNULL(p_id) THEN 'Root'
+    WHEN (id NOT IN (SELECT IFNULL(p_id, 0) FROM Tree)) THEN 'Leaf'
+    ELSE 'Inner'
+    END
+) AS type FROM Tree
diff --git a/Problem 4.sql b/Problem 4.sql
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+++ b/Problem 4.sql	
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+# Write your MySQL query statement below
+WITH CTE AS (
+    SELECT *, DENSE_RANK() OVER(PARTITION BY departmentId ORDER BY salary DESC) AS rnk FROM Employee
+),
+CTE2 AS (
+    SELECT * FROM CTE WHERE rnk<=3
+)
+SELECT d.name AS Department, CTE2.name AS Employee, CTE2.salary AS Salary 
+FROM CTE2 JOIN Department d ON CTE2.departmentId=d.id
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