Solutions to Sql3 problems

problem_1_consecutive_numbers.sql

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+SELECT DISTINCT l1.num as ConsecutiveNums
+FROM Logs l1 
+    JOIN Logs l2 ON (l1.id = l2.id - 1) AND (l1.num = l2.num)
+    JOIN Logs l3 ON (l2.id = l3.id - 1) AND (l2.num = l3.num);

problem_2_count_passengers.sql

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+with cte as (
+    SELECT p.passenger_id, p.arrival_time, min(b.arrival_time) as boarding_time
+    FROM passengers p 
+    JOIN buses b
+    on p.arrival_time <= b.arrival_time
+    GROUP BY p.passenger_id, p.arrival_time
+
+)
+
+SELECT b.bus_id, count(boarding_time) as passengers_cnt
+FROM buses b
+LEFT JOIN cte
+on b.arrival_time = cte.boarding_time
+GROUP BY bus_id
+ORDER BY bus_id

problem_3_active_users.sql

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+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

problem_4_dynamic_pivot.sql

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+CREATE PROCEDURE PivotProducts()
+BEGIN
+	set session group_concat_max_len = 1000000; # default is 1024
+
+	set @sql = null;
+	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