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            "questionId": "1245",
            "questionFrontendId": "1141",
            "boundTopicId": null,
            "title": "User Activity for the Past 30 Days I",
            "titleSlug": "user-activity-for-the-past-30-days-i",
            "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 (&#39;open_session&#39;, &#39;end_session&#39;, &#39;scroll_down&#39;, &#39;send_message&#39;).\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>&nbsp;</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>&nbsp;</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\"]]}}",
            "categoryTitle": "Database",
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            "codeSnippets": [
                {
                    "lang": "MySQL",
                    "langSlug": "mysql",
                    "code": "# Write your MySQL query statement below\n",
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                },
                {
                    "lang": "MS SQL Server",
                    "langSlug": "mssql",
                    "code": "/* Write your T-SQL query statement below */\n",
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                },
                {
                    "lang": "Oracle",
                    "langSlug": "oraclesql",
                    "code": "/* Write your PL/SQL query statement below */\n",
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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\"]]}}",
            "metaData": "{\n  \"mysql\": [\n    \"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'))\"\n  ],\n  \"mssql\": [\n    \"create table Activity (user_id int, session_id int, activity_date date, activity_type varchar(15) not null check(activity_type in ('open_session', 'end_session', 'scroll_down', 'send_message')))\"\n  ],\n  \"oraclesql\": [\n    \"create table Activity (user_id int, session_id int, activity_date date, activity_type varchar(15) not null check(activity_type in ('open_session', 'end_session', 'scroll_down', 'send_message')))\",\n    \"ALTER SESSION SET nls_date_format='YYYY-MM-DD'\"\n  ],\n  \"database\": true\n}",
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            "mysqlSchemas": [
                "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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            "envInfo": "{\"mysql\": [\"MySQL\", \"<p><code>MySQL 8.0</code>.</p>\"], \"mssql\": [\"MS SQL Server\", \"<p><code>mssql server 2019</code>.</p>\"], \"oraclesql\": [\"Oracle\", \"<p><code>Oracle Sql 11.2</code>.</p>\"]}",
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