SQL3: First 3 Problems solved

consecutive_numbers

@@ -0,0 +1,9 @@
+SELECT  DISTINCT num AS ConsecutiveNums
+FROM (
+    SELECT  num,
+            LEAD(num,1) OVER(ORDER BY id) second_num,
+            LEAD(num,2) OVER(ORDER BY id) third_num
+    FROM logs
+    ) a
+WHERE num = second_num
+AND num = third_num;

num_of_passengers

@@ -0,0 +1,15 @@
+WITH cte AS (
+    SELECT  p.passenger_id,
+            p.arrival_time AS p_time,
+            MIN(b.arrival_time) AS b_time
+    FROM passengers p
+    INNER JOIN buses b
+    ON p.arrival_time <= b.arrival_time
+    GROUP BY 1
+)
+SELECT  b.bus_id,
+        IFNULL(COUNT(c.passenger_id),0) AS passengers_cnt
+FROM buses b
+LEFT JOIN cte c
+on b.arrival_time = c.b_time
+GROUP BY 1;

user_activity

@@ -0,0 +1,7 @@
+SELECT  activity_date AS day,
+        COUNT(DISTINCT user_id) AS active_users
+FROM activity
+WHERE activity_type IS NOT NULL
+AND DATEDIFF('2019-07-27',activity_date) < 30
+AND DATEDIFF('2019-07-27',activity_date) >= 0
+GROUP BY activity_date;