add 1141

fishercoder1534 · fishercoder1534 · commit c0a1c0986fbd · 2020-02-01T12:05:14.000-08:00
diff --git a/README.md b/README.md
@@ -854,6 +854,7 @@ _If you like this project, please leave me a star._ &#9733;
 |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 |
+|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 |
 |1084|[Sales Analysis III](https://leetcode.com/problems/sales-analysis-iii/)|[Solution](../master/database/_1084.sql) |  | Easy |
 |1083|[Sales Analysis II](https://leetcode.com/problems/sales-analysis-ii/)|[Solution](../master/database/_1083.sql) |  | Easy |
 |1082|[Sales Analysis I](https://leetcode.com/problems/sales-analysis-i/)|[Solution](../master/database/_1082.sql) |  | Easy |
diff --git a/database/_1141.sql b/database/_1141.sql
@@ -0,0 +1,52 @@
+--1141. User Activity for the Past 30 Days I
+--
+--Table: Activity
+--
+--+---------------+---------+
+--| Column Name   | Type    |
+--+---------------+---------+
+--| user_id       | int     |
+--| session_id    | int     |
+--| activity_date | date    |
+--| activity_type | enum    |
+--+---------------+---------+
+--There is no primary key for this table, it may have duplicate rows.
+--The activity_type column is an ENUM of type ('open_session', 'end_session', 'scroll_down', 'send_message').
+--The table shows the user activities for a social media website.
+--Note that each session belongs to exactly one user.
+--
+--
+--Write an SQL query to find the daily active user count for a period of 30 days ending 2019-07-27 inclusively. A user was active on some day if he/she made at least one activity on that day.
+--
+--The query result format is in the following example:
+--
+--Activity table:
+--+---------+------------+---------------+---------------+
+--| user_id | session_id | activity_date | activity_type |
+--+---------+------------+---------------+---------------+
+--| 1       | 1          | 2019-07-20    | open_session  |
+--| 1       | 1          | 2019-07-20    | scroll_down   |
+--| 1       | 1          | 2019-07-20    | end_session   |
+--| 2       | 4          | 2019-07-20    | open_session  |
+--| 2       | 4          | 2019-07-21    | send_message  |
+--| 2       | 4          | 2019-07-21    | end_session   |
+--| 3       | 2          | 2019-07-21    | open_session  |
+--| 3       | 2          | 2019-07-21    | send_message  |
+--| 3       | 2          | 2019-07-21    | end_session   |
+--| 4       | 3          | 2019-06-25    | open_session  |
+--| 4       | 3          | 2019-06-25    | end_session   |
+--+---------+------------+---------------+---------------+
+--
+--Result table:
+--+------------+--------------+
+--| day        | active_users |
+--+------------+--------------+
+--| 2019-07-20 | 2            |
+--| 2019-07-21 | 2            |
+--+------------+--------------+
+--Note that we do not care about days with zero active users.
+
+--# Write your MySQL query statement below
+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;
