SQL2

Rankemails.sql

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+# Write your MySQL query statement below
+# -------------------------- Using Window Function DENSE_RANK()--------------
+-- SELECT 
+--     Score,
+--     DENSE_RANK() OVER (ORDER BY Score DESC) AS 'rank'
+-- FROM 
+--     Scores;
+
+# ------------------------- Handling Null with Null as rank 1 -----------------
+SELECT 
+    Score,
+    DENSE_RANK() OVER (ORDER BY COALESCE(Score, 1) DESC) AS 'RANK'
+FROM 
+    Scores;
+
+# ------------------------- Using subquery-------------------------------
+-- SELECT 
+--     Score,
+--     (SELECT COUNT(DISTINCT Score)
+--     FROM scores s2
+--     WHERE s2.score >= s1.score
+--     ) AS 'rank'
+-- FROM
+--     Scores s1
+-- ORDER BY
+--     score DESC;

Top3Dept.sql

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+WITH RankedSalaries AS (
+    SELECT 
+        d.name AS Department,
+        e.name AS Employee,
+        e.salary AS Salary,
+        DENSE_RANK() OVER (PARTITION BY e.departmentId ORDER BY e.salary DESC) AS salary_rank
+    FROM Employee e
+    JOIN Department d ON e.departmentId = d.id
+)
+SELECT 
+    Department,
+    Employee,
+    Salary
+FROM RankedSalaries
+WHERE salary_rank <= 3;

TreeNode.sql

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+# Write your MySQL query statement below
+SELECT
+    id, 'Root' as Type
+FROM
+    Tree 
+WHERE p_id IS NULL
+UNION
+SELECT
+    id, 'Leaf' as Type
+FROM
+    Tree
+WHERE id NOT IN (
+    SELECT 
+        DISTINCT p_id
+    FROM
+        Tree
+    WHERE p_id IS NOT NULL
+) AND
+p_id IS NOT NULL
+UNION
+SELECT
+    id, 'Inner' as Type
+FROM
+    Tree
+WHERE id IN (
+    SELECT
+        DISTINCT p_id
+    FROM
+        Tree
+    WHERE p_id IS NOT NULL
+) AND
+p_id IS NOT NULL;

exchangeSeats.sql

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+# Write your MySQL query statement below
+#-------------------Using ODD/EVEN ---------------
+-- SELECT(
+--     CASE 
+--         WHEN mod(id, 2) != 0 AND id != cnt THEN id + 1
+--         WHEN mod(id, 2) != 0 AND id = cnt THEN id
+--         ELSE id - 1
+--     END) AS id, student 
+--     FROM 
+--         Seat, (SELECT COUNT(*) AS cnt FROM Seat) as count_table
+--     ORDER BY id 
+#---------------- Using LEFT JOIN and XOR function------------------
+SELECT 
+    s1.id, COALESCE(s2.student, s1.student) AS 'student'
+FROM
+    Seat s1 
+    LEFT JOIN
+    Seat s2
+    ON
+    (s1.id + 1) ^ 1 - 1 = s2.id
+ORDER BY
+    s1.id