diff --git a/1.sql b/1.sql
new file mode 100644
index 0000000..1eae7cb
--- /dev/null
+++ b/1.sql
@@ -0,0 +1,8 @@
+# Write your MySQL query statement below
+WITH CTE AS (
+    SELECT score,
+        DENSE_RANK() OVER (ORDER BY score DESC) AS rnk
+    FROM Scores
+)
+SELECT score, rnk AS 'rank'
+FROM CTE
\ No newline at end of file
diff --git a/2.sql b/2.sql
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--- /dev/null
+++ b/2.sql
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+SELECT (
+    CASE 
+        WHEN id%2 != 0 AND id = cnt THEN id
+        WHEN id%2 != 0 AND id != cnt THEN id+1
+        ELSE id-1
+    END
+) AS 'id', student FROM Seat , (SELECT COUNT(*) AS 'cnt' FROM Seat) AS seat_counts ORDER BY id
diff --git a/3.sql b/3.sql
new file mode 100644
index 0000000..82a3f33
--- /dev/null
+++ b/3.sql
@@ -0,0 +1,8 @@
+SELECT id, (
+    CASE 
+        WHEN p_id IS NULL THEN 'Root' 
+        WHEN id NOT IN (SELECT DISTINCT p_id FROM Tree WHERE p_id IS NOT NULL) AND p_id IS NOT NULL THEN 'Leaf' 
+        ELSE 'Inner' 
+    END     
+) AS type
+FROM Tree
\ No newline at end of file
diff --git a/4.sql b/4.sql
new file mode 100644
index 0000000..65cc4c3
--- /dev/null
+++ b/4.sql
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+WITH CTE AS(
+    SELECT Employee.name, Employee.departmentId, salary, DENSE_RANK() 
+OVER (PARTITION BY Employee.departmentId ORDER BY Employee.salary DESC) AS rnk
+FROM Employee)
+
+
+SELECT Department.name AS Department, CTE.name AS Employee, CTE.salary AS Salary
+FROM CTE
+JOIN Department ON Department.id = CTE.departmentId
+WHERE rnk <= 3
+