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"questionId": "1245",
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"title": "User Activity for the Past 30 Days I",
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"content": "<p>Table: <code>Activity</code></p>\n\n<pre>\n+---------------+---------+\n| Column Name | Type |\n+---------------+---------+\n| user_id | int |\n| session_id | int |\n| activity_date | date |\n| activity_type | enum |\n+---------------+---------+\nThere is no primary key for this table, it may have duplicate rows.\nThe activity_type column is an ENUM of type ('open_session', 'end_session', 'scroll_down', 'send_message').\nThe table shows the user activities for a social media website. \nNote that each session belongs to exactly one user.\n</pre>\n\n<p> </p>\n\n<p>Write an SQL query to find the daily active user count for a period of <code>30</code> days ending <code>2019-07-27</code> inclusively. A user was active on someday if they made at least one activity on that day.</p>\n\n<p>Return the result table in <strong>any order</strong>.</p>\n\n<p>The query result format is in the following example.</p>\n\n<p> </p>\n<p><strong>Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> \nActivity table:\n+---------+------------+---------------+---------------+\n| user_id | session_id | activity_date | activity_type |\n+---------+------------+---------------+---------------+\n| 1 | 1 | 2019-07-20 | open_session |\n| 1 | 1 | 2019-07-20 | scroll_down |\n| 1 | 1 | 2019-07-20 | end_session |\n| 2 | 4 | 2019-07-20 | open_session |\n| 2 | 4 | 2019-07-21 | send_message |\n| 2 | 4 | 2019-07-21 | end_session |\n| 3 | 2 | 2019-07-21 | open_session |\n| 3 | 2 | 2019-07-21 | send_message |\n| 3 | 2 | 2019-07-21 | end_session |\n| 4 | 3 | 2019-06-25 | open_session |\n| 4 | 3 | 2019-06-25 | end_session |\n+---------+------------+---------------+---------------+\n<strong>Output:</strong> \n+------------+--------------+ \n| day | active_users |\n+------------+--------------+ \n| 2019-07-20 | 2 |\n| 2019-07-21 | 2 |\n+------------+--------------+ \n<strong>Explanation:</strong> Note that we do not care about days with zero active users.\n</pre>\n",
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"exampleTestcases": "{\"headers\":{\"Activity\":[\"user_id\",\"session_id\",\"activity_date\",\"activity_type\"]},\"rows\":{\"Activity\":[[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\"]]}}",
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"lang": "MySQL",
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"code": "# Write your MySQL query statement below\n",
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"lang": "MS SQL Server",
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"sampleTestCase": "{\"headers\":{\"Activity\":[\"user_id\",\"session_id\",\"activity_date\",\"activity_type\"]},\"rows\":{\"Activity\":[[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\"]]}}",
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"Create table If Not Exists Activity (user_id int, session_id int, activity_date date, activity_type ENUM('open_session', 'end_session', 'scroll_down', 'send_message'))",
"Truncate table Activity",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('1', '1', '2019-07-20', 'open_session')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('1', '1', '2019-07-20', 'scroll_down')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('1', '1', '2019-07-20', 'end_session')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('2', '4', '2019-07-20', 'open_session')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('2', '4', '2019-07-21', 'send_message')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('2', '4', '2019-07-21', 'end_session')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('3', '2', '2019-07-21', 'open_session')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('3', '2', '2019-07-21', 'send_message')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('3', '2', '2019-07-21', 'end_session')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('4', '3', '2019-06-25', 'open_session')",
"insert into Activity (user_id, session_id, activity_date, activity_type) values ('4', '3', '2019-06-25', 'end_session')"
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