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+1 Problem 1 : Consecutive Numbers (https://leetcode.com/problems/consecutive-numbers/)
+
+# Write your MySQL query statement below
+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;
+
+2 Problem 2 :Number of Passengers in Each Bus ( https://leetcode.com/problems/the-number-of-passengers-in-each-bus-i/ )
+
+with cte as 
+(select b.bus_id, p.passenger_id, p.arrival_time, min(b.arrival_time) as 'btime' from Passengers p INNER JOIN Buses b on p.arrival_time <= b.arrival_time group by p.passenger_id)
+
+select b.bus_id, count(c.btime) as 'passengers_cnt' from Buses b left join cte c on b.arrival_time = c.btime group by b.bus_id order by b.bus_id;
+
+
+
+3 Problem 3 :User Activity (https://leetcode.com/problems/user-activity-for-the-past-30-days-i/ )
+
+select activity_date as 'day', count(distinct user_id) as 'active_users' from Activity where activity_date > '2019-06-27'AND activity_date <= '2019-06-27' group by activity_date;
+
+
+
+4 Problem 4 :Dynamic Pivoting of a Table ( https://leetcode.com/problems/dynamic-pivoting-of-a-table/ )
+
+SET @sql = NULL;
+
+SELECT GROUP_CONCAT(
+         DISTINCT CONCAT(
+           'MAX(CASE WHEN course_id = ', course_id, 
+           ' THEN grade END) AS `', course_id, '`'
+         )
+       )
+INTO @sql
+FROM Scores;
+
+SET @sql = CONCAT('SELECT student_id, ', @sql, ' FROM Scores GROUP BY student_id');
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+
+
+