Complete SQL2

README.md

@@ -2,8 +2,60 @@
 
 Problem 1 : Rank Scores		(https://leetcode.com/problems/rank-scores/ )
 
+
 Problem 2 : Exchange Seats	(https://leetcode.com/problems/exchange-seats/ )
 
 Problem 3 : Tree Node		(https://leetcode.com/problems/tree-node/ )
 
 Problem 4 : Deparment Top 3 Salaries		(https://leetcode.com/problems/department-top-three-salaries/ )
+
+
+Problem 1 : Rank Scores		(https://leetcode.com/problems/rank-scores/ )
+
+SELECT 
+    score,
+    DENSE_RANK() OVER (ORDER BY score DESC) AS 'rank'
+FROM 
+    Scores;
+
+
+Problem 2 : Exchange Seats	(https://leetcode.com/problems/exchange-seats/ )
+
+SELECT 
+    CASE
+        WHEN id % 2 = 1 AND id + 1 <= (SELECT MAX(id) FROM Seat) THEN id + 1
+        WHEN id % 2 = 0 THEN id - 1
+        ELSE id
+    END AS id,
+    student
+FROM Seat
+ORDER BY id;
+
+
+Problem 3 : Tree Node		(https://leetcode.com/problems/tree-node/ )
+
+SELECT 
+    t1.id,
+    CASE 
+        WHEN t1.p_id IS NULL THEN 'Root'
+        WHEN t1.id IN (SELECT DISTINCT p_id FROM Tree WHERE p_id IS NOT NULL) THEN 'Inner'
+        ELSE 'Leaf'
+    END AS type
+FROM Tree t1;
+
+
+
+Problem 4 : Deparment Top 3 Salaries		(https://leetcode.com/problems/department-top-three-salaries/ )
+
+SELECT 
+    d.name AS Department,
+    e.name AS Employee,
+    e.salary AS Salary
+FROM (
+    SELECT *,
+           DENSE_RANK() OVER (PARTITION BY departmentId ORDER BY salary DESC) AS rnk
+    FROM Employee
+) e
+JOIN Department d ON e.departmentId = d.id
+WHERE rnk <= 3;
+