Done Sql3 (except 4th question)

Sql3.sql

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+# 1 Problem 1 : Consecutive Numbers (https://leetcode.com/problems/consecutive-numbers/)
+
+# Solution
+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/ )
+
+# Solution
+WITH CTE AS
+(
+    SELECT p.passenger_id, p.arrival_time, MIN(b.arrival_time) AS btime
+    FROM Buses b
+    JOIN Passengers p
+    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 c.btime = b.arrival_time
+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/ )
+
+# 1st Solution
+SELECT activity_date AS day, COUNT(DISTINCT user_id) AS active_users
+FROM Activity 
+WHERE activity_date BETWEEN '2019-06-28' AND '2019-07-27'
+GROUP BY activity_date
+
+# 2nd Solution
+SELECT activity_date AS day, COUNT(DISTINCT user_id) AS active_users
+FROM Activity 
+WHERE activity_date >= '2019-06-28' AND activity_date <= '2019-07-27'
+GROUP BY activity_date
+
+# 3rd Solution
+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
+
+# 4th Solution
+SELECT activity_date AS day, COUNT(DISTINCT user_id) AS active_users
+FROM Activity
+WHERE activity_date BETWEEN date_sub('2019-07-27', INTERVAL 29 DAY) AND '2019-07-27'
+GROUP BY activity_date
+
+# 5th Solution
+SELECT activity_date AS day, COUNT(DISTINCT user_id) AS active_users
+FROM Activity
+WHERE activity_date BETWEEN date_add('2019-07-27', INTERVAL -29 DAY) AND '2019-07-27'
+GROUP BY activity_date
+
+# 4 Problem 4 :Dynamic Pivoting of a Table ( https://leetcode.com/problems/dynamic-pivoting-of-a-table/ )
+# Not done in Class yet.