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Author: mrinal1704

Medium/Get the second most recent activity.sql

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+-- Question 109
+-- Table: UserActivity
+
+-- +---------------+---------+
+-- | Column Name   | Type    |
+-- +---------------+---------+
+-- | username      | varchar |
+-- | activity      | varchar |
+-- | startDate     | Date    |
+-- | endDate       | Date    |
+-- +---------------+---------+
+-- This table does not contain primary key.
+-- This table contain information about the activity performed of each user in a period of time.
+-- A person with username performed a activity from startDate to endDate.
+
+-- Write an SQL query to show the second most recent activity of each user.
+
+-- If the user only has one activity, return that one. 
+
+-- A user can't perform more than one activity at the same time. Return the result table in any order.
+
+-- The query result format is in the following example:
+
+-- UserActivity table:
+-- +------------+--------------+-------------+-------------+
+-- | username   | activity     | startDate   | endDate     |
+-- +------------+--------------+-------------+-------------+
+-- | Alice      | Travel       | 2020-02-12  | 2020-02-20  |
+-- | Alice      | Dancing      | 2020-02-21  | 2020-02-23  |
+-- | Alice      | Travel       | 2020-02-24  | 2020-02-28  |
+-- | Bob        | Travel       | 2020-02-11  | 2020-02-18  |
+-- +------------+--------------+-------------+-------------+
+
+-- Result table:
+-- +------------+--------------+-------------+-------------+
+-- | username   | activity     | startDate   | endDate     |
+-- +------------+--------------+-------------+-------------+
+-- | Alice      | Dancing      | 2020-02-21  | 2020-02-23  |
+-- | Bob        | Travel       | 2020-02-11  | 2020-02-18  |
+-- +------------+--------------+-------------+-------------+
+
+-- The most recent activity of Alice is Travel from 2020-02-24 to 2020-02-28, before that she was dancing from 2020-02-21 to 2020-02-23.
+-- Bob only has one record, we just take that one.
+
+-- Solution
+select username, activity, startdate, enddate
+from
+(select *,
+rank() over(partition by username order by startdate desc) as rk,
+count(username) over(partition by username) as cnt
+from useractivity) a
+where a.rk = 2 or cnt = 1