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Commit0d19238

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add 511
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‎README.md

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@@ -835,6 +835,7 @@ Your ideas/fixes/algorithms are more than welcome!
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|571|[Find Median Given Frequency of Numbers](https://leetcode.com/problems/find-median-given-frequency-of-numbers/)|[Solution](../master/database/_571.sql)||| Hard|
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|570|[Managers with at Least 5 Direct Reports](https://leetcode.com/problems/managers-with-at-least-5-direct-reports/)|[Solution](../master/database/_570.sql)||| Medium|
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|569|[Median Employee Salary](https://leetcode.com/problems/median-employee-salary/)|[Solution](../master/database/_569.sql)||| Hard|
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|511|[Game Play Analysis I](https://leetcode.com/problems/game-play-analysis-i/)|[Solution](../master/database/_511.sql)||| Easy|
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|262|[Trips and Users](https://leetcode.com/problems/trips-and-users/)|[Solution](../master/database/_262.sql)||| Hard| Inner Join
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|197|[Rising Temperature](https://leetcode.com/problems/rising-temperature/)|[Solution](../master/database/_197.sql)| O(n^2)|O(n)| Easy|
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|196|[Delete Duplicate Emails](https://leetcode.com/problems/delete-duplicate-emails/)|[Solution](../master/database/_196.sql)| O(n^2)|O(n)| Easy|

‎database/_511.sql

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--511. Game Play Analysis I
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--
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--Table: Activity
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--
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--+--------------+---------+
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--| Column Name | Type |
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--+--------------+---------+
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--| player_id | int |
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--| device_id | int |
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--| event_date | date |
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--| games_played | int |
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--+--------------+---------+
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--(player_id, event_date) is the primary key of this table.
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--This table shows the activity of players of some game.
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--Each row is a record of a player who logged in and played a number of games (possibly 0) before logging out on some day using some device.
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--
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--
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--Write an SQL query that reports the first login date for each player.
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--
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--The query result format is in the following example:
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--
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--Activity table:
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--+-----------+-----------+------------+--------------+
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--| player_id | device_id | event_date | games_played |
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--+-----------+-----------+------------+--------------+
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--| 1 | 2 | 2016-03-01 | 5 |
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--| 1 | 2 | 2016-05-02 | 6 |
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--| 2 | 3 | 2017-06-25 | 1 |
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--| 3 | 1 | 2016-03-02 | 0 |
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--| 3 | 4 | 2018-07-03 | 5 |
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--+-----------+-----------+------------+--------------+
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--
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--Result table:
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--+-----------+-------------+
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--| player_id | first_login |
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--+-----------+-------------+
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--| 1 | 2016-03-01 |
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--| 2 | 2017-06-25 |
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--| 3 | 2016-03-02 |
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--+-----------+-------------+
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--# Write your MySQL query statement below
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select player_id,min(event_date)as first_login
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from Activity
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group by player_id

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