Completed solution_sql3.sql

solution_sql3.sql

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+-- Solution to Problem 1
+SELECT DISTINCT l1.num AS 'ConsecutiveNums'
+FROM Logs l1, Logs l2, Logs l3
+WHERE l1.id = l2.id - 1 AND l2.id = l3.id - 1
+AND l1.num = l2.num AND l2.num = l3.num
+
+-- Solution to Problem 1 (Using window function)
+WITH CTE_leads AS (
+    SELECT id, LEAD(id, 1) OVER (ORDER BY id) AS id_lead1, LEAD(id, 2) OVER (ORDER BY id) AS id_lead2,  
+        num, LEAD(num, 1) OVER (ORDER BY id) AS lead1, LEAD(num, 2) OVER (ORDER BY id) AS lead2
+    FROM Logs
+)
+
+SELECT DISTINCT num AS 'ConsecutiveNums'
+FROM CTE_leads
+WHERE num = lead1 AND num = lead2
+AND id = id_lead1 - 1 AND id = id_lead2 - 2
+
+-- Solution to Problem 2
+WITH CTE_times AS (
+    SELECT p.passenger_id, p.arrival_time, MIN(b.arrival_time) as 'bus_time'
+    FROM Passengers p
+    LEFT JOIN Buses b
+    ON p.arrival_time <= b.arrival_time
+    GROUP BY p.passenger_id
+)
+SELECT b.bus_id, COUNT(c.bus_time) AS 'passengers_cnt'
+FROM Buses b
+LEFT JOIN CTE_times c ON b.arrival_time = c.bus_time
+GROUP BY b.bus_id ORDER BY b.bus_id
+
+-- Solution to Problem 3
+SELECT activity_date as 'day', COUNT(DISTINCT user_id) AS active_users
+FROM Activity
+WHERE activity_date > '2019-06-27' AND activity_date <= '2019-07-27'
+GROUP BY activity_date
+
+-- Solution to Problem 4
+CREATE PROCEDURE PivotProducts()
+BEGIN
+    SET SESSION GROUP_CONCAT_MAX_LEN = 1000000;
+    SELECT GROUP_CONCAT(DISTINCT CONCAT('SUM(IF(store = "', store, '", price, null)) AS ', store)) 
+    INTO @sql FROM products;
+
+    SET @sql = CONCAT('SELECT product_id, ', @sql, ' FROM Products GROUP BY 1');
+
+    PREPARE stmt FROM @sql;
+    EXECUTE stmt;
+    DEALLOCATE PREPARE stmt;
+END;