SQL 3

Problem 4 Dynamic Pivoting of a Table.sql

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+CREATE PROCEDURE PivotProducts()
+BEGIN
+
+    SET SESSION GROUP_CONCAT_MAX_LEN =  1000000;
+    # Step 1: Generate dynamic SQL for pivot columns
+    SELECT GROUP_CONCAT(DISTINCT CONCAT('SUM(IF(store = "', store, '", price, NULL)) AS `', store, '`')) INTO @sql
+    FROM products;
+
+    # Step 2: Construct the complete dynamic SQL query
+    SET @sql = CONCAT(
+        'SELECT product_id, ', 
+        @sql, 
+        ' FROM products GROUP BY product_id'
+    );
+    # Step 3: Prepare and execute the dynamic SQL
+    PREPARE stmt FROM @sql;
+    EXECUTE stmt;
+    DEALLOCATE PREPARE stmt;
+
+END

Problem1ConsecutiveNumebrs.sql

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+# Write your MySQL query statement below
+-- Step 1: Create a Common Table Expression (CTE) to compare the current row with the next two rows
+WITH ConsecutiveNumsCTE AS (
+    SELECT 
+        l1.id AS CurrentID,        -- ID of the current row
+        l1.num AS CurrentNum,      -- Number of the current row
+        l2.num AS NextNum,         -- Number from the next row
+        l3.num AS SecondNextNum    -- Number from the second next row
+    FROM Logs l1
+    -- Join the table with itself to get the next row (ID = CurrentID + 1)
+    LEFT JOIN Logs l2
+        ON l1.id = l2.id - 1
+    -- Join the table again to get the second next row (ID = CurrentID + 2)
+    LEFT JOIN Logs l3
+        ON l1.id = l3.id - 2
+)
+
+-- Step 2: Select numbers that appear three times consecutively
+SELECT DISTINCT CurrentNum AS ConsecutiveNums
+FROM ConsecutiveNumsCTE
+-- Filter rows where the current number is equal to both the next and the second next number
+WHERE CurrentNum = NextNum AND NextNum = SecondNextNum;

Problem2PassengersinEachBus.sql

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+WITH BusTime AS (
+    SELECT bus_id, arrival_time, LAG(arrival_time,1,0) OVER (ORDER BY arrival_time) AS previous_arrival_time 
+FROM Buses
+),
+FinalArrivalTime AS (
+SELECT b.bus_id, p.passenger_id
+FROM BusTime b
+LEFT JOIN Passengers p
+ON p.arrival_time>b.previous_arrival_time AND p.arrival_time<=b.arrival_time
+)
+
+
+SELECT f.bus_id, COUNT(f.passenger_id) AS passengers_cnt
+FROM FinalArrivalTime f
+GROUP BY f.bus_id
+ORDER BY f.bus_id

Problem3User Activity.sql

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+WITH CTE AS (
+    SELECT DISTINCT activity_date as day, user_id FROM Activity
+WHERE activity_date BETWEEN DATE_ADD( '2019-07-27' , INTERVAL -29 DAY) AND '2019-07-27'  
+)
+
+SELECT CTE.day, COUNT(DISTINCT user_id) AS active_users
+FROM CTE
+GROUP BY CTE.day