add 1142

Author: fishercoder1534

Diff for: README.md

@@ -1138,6 +1138,7 @@ _If you like this project, please leave me a star._ ★
 |1179|[Reformat Department Table](https://leetcode.com/problems/reformat-department-table/)|[Solution](../master/database/_1179.sql) |  | Easy |
 |1173|[Immediate Food Delivery I](https://leetcode.com/problems/immediate-food-delivery-i/)|[Solution](../master/database/_1173.sql) |  | Easy |
 |1148|[Article Views I](https://leetcode.com/problems/article-views-i/)|[Solution](../master/database/_1148.sql) |  | Easy |
+|1142|[User Activity for the Past 30 Days II](https://leetcode.com/problems/user-activity-for-the-past-30-days-ii/)|[Solution](../master/database/_1142.sql) |  | Easy |
 |1141|[User Activity for the Past 30 Days I](https://leetcode.com/problems/user-activity-for-the-past-30-days-i/)|[Solution](../master/database/_1141.sql) |  | Easy |
 |1113|[Reported Posts](https://leetcode.com/problems/reported-posts/)|[Solution](../master/database/_1113.sql) |  | Easy |
 |1084|[Sales Analysis III](https://leetcode.com/problems/sales-analysis-iii/)|[Solution](../master/database/_1084.sql) |  | Easy |

Diff for: database/_1142.sql

@@ -0,0 +1,5 @@
+--# Write your MySQL query statement below
+select ifnull(round(count(distinct session_id)/count(distinct user_id), 2), 0.00)
+as average_sessions_per_user
+from Activity
+where activity_date between '2019-06-28' and '2019-07-27';