✅No SubQuery | Easy to understand solution using CTEs | O(N)
Intuition\n Describe your first thoughts on how to solve this problem. \nTo determine the fraction of players who log in exactly one day after their first login
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\nTo determine the fraction of players who log in exactly one day after their first login, we need to track the first login date for each player and then check if there are subsequent logins exactly one day after that date. This involves calculating the date difference between the login events and the first login date.\n\n---\n# Approach\n<!-- Describe your approach to solving the problem. -->\n1. **Calculate First Login Date**: Use a Common Table Expression (CTE) to calculate and store the first login date for each player.\n2. **Join with Activity**: Join the original `Activity` table with the CTE on `player_id` to access both the login events and the first login date.\n3. **Calculate Date Difference**: Use the `DATEDIFF` function to check if the event date is exactly one day after the first login date.\n4. **Aggregate Results**: Sum up the cases where the condition is true and divide by the total number of unique players to get the desired fraction. Round the result to two decimal places.\n---\n# Code\n```sql\n# Write your MySQL query statement below\n\n# First, let\'s store the first login date of each player.\nWITH temp AS (\n    SELECT player_id, MIN(event_date) AS first_login_date\n    FROM Activity \n    GROUP BY player_id\n)\n\n# Calculate the fraction of players who logged in exactly one day after their first login.\nSELECT \n    ROUND(\n        SUM(DATEDIFF(a.event_date, t.first_login_date) = 1) / COUNT(DISTINCT a.player_id), 2\n    ) AS fraction\nFROM Activity a\nJOIN temp t ON a.player_id = t.player_id;\n```\n----\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\nThe time complexity is $$O(n)$$, where $$n$$ is the number of rows in the `Activity` table. This is because the query processes each row in the `Activity` table to calculate the first login date and checks the date difference for each login event.\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\nThe space complexity is $$O(n)$$, where $$n$$ is the number of players, because the CTE `temp` will store the first login date for each player.\n\n---\n
['MySQL']