1890. The Latest Login in 2020

Description

Table: Logins

+----------------+----------+
| Column Name    | Type     |
+----------------+----------+
| user_id        | int      |
| time_stamp     | datetime |
+----------------+----------+
(user_id, time_stamp) is the primary key (combination of columns with unique values) for this table.
Each row contains information about the login time for the user with ID user_id.

Write a solution to report the latest login for all users in the year 2020. Do not include the users who did not login in 2020.

Return the result table in any order.

The result format is in the following example.

Example 1:

Input: 
Logins table:
+---------+---------------------+
| user_id | time_stamp          |
+---------+---------------------+
| 6       | 2020-06-30 15:06:07 |
| 6       | 2021-04-21 14:06:06 |
| 6       | 2019-03-07 00:18:15 |
| 8       | 2020-02-01 05:10:53 |
| 8       | 2020-12-30 00:46:50 |
| 2       | 2020-01-16 02:49:50 |
| 2       | 2019-08-25 07:59:08 |
| 14      | 2019-07-14 09:00:00 |
| 14      | 2021-01-06 11:59:59 |
+---------+---------------------+
Output: 
+---------+---------------------+
| user_id | last_stamp          |
+---------+---------------------+
| 6       | 2020-06-30 15:06:07 |
| 8       | 2020-12-30 00:46:50 |
| 2       | 2020-01-16 02:49:50 |
+---------+---------------------+
Explanation: 
User 6 logged into their account 3 times but only once in 2020, so we include this login in the result table.
User 8 logged into their account 2 times in 2020, once in February and once in December. We include only the latest one (December) in the result table.
User 2 logged into their account 2 times but only once in 2020, so we include this login in the result table.
User 14 did not login in 2020, so we do not include them in the result table.

Solutions

Solution 1: Group By + Max Function

We can first filter out the login records in 2020, and then group by user_id, and use the max function to calculate the maximum login time for each user.

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# Write your MySQL query statement below
SELECT user_id, MAX(time_stamp) AS last_stamp
FROM Logins
WHERE YEAR(time_stamp) = 2020
GROUP BY 1;