Day three did three sums, Dynamic Pivoting is Left

Problem1.sql

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+# Write your MySQL query statement below
+select distinct(num) as consecutiveNums
+from (
+    select id,num,
+    lag(num) over(order by id) as pervious_num,
+    lead(num) over(order by id) as next_num
+    from logs
+) sq
+where sq.num=sq.pervious_num and sq.num=sq.next_num;

Problem2.sql

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+SELECT b.id AS bus_id, COUNT(p.passenger_id) AS passengers_cnt
+FROM Buses b
+LEFT JOIN (
+    SELECT p.passenger_id, MIN(b.id) AS bb
+    FROM Passengers p
+    JOIN Buses b ON p.arrival_time <= b.arrival_time
+    GROUP BY p.passenger_id
+) AS p ON b.id = p.bb
+GROUP BY b.id
+ORDER BY b.id;

README.md

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 # Sql3
 
-1 Problem 1 : Consecutive Numbers	(https://leetcode.com/problems/consecutive-numbers/)
+Problem 1  : Consecutive Numbers	(https://leetcode.com/problems/consecutive-numbers/)
 
 2 Problem 2 :Number of Passengers in Each Bus 	(	https://leetcode.com/problems/the-number-of-passengers-in-each-bus-i/ )
 

problem3.sql

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+# Write your MySQL query statement below
+select activity_date as day,count(DISTINCT user_id) as active_users
+from Activity
+where datediff('2019-07-27',activity_date) <30
+and activity_date <= '2019-07-27'
+group by activity_date;