SQL query for the last login record date for each user

question:

Suppose the database table contains user login information, how do we retrieve the last login date for each user? Considering that there may be duplicate login dates.

Solution:

There are two common ways to solve this problem:

Method 1: Subquery using INNER JOIN

This method uses a subquery to identify the last login date for each user and is then used to filter the main table:

select t.username, t.date, t.value
from MyTable t
inner join (
    select username, max(date) as MaxDate
    from MyTable
    group by username
) tm on t.username = tm.username and t.date = tm.MaxDate

Method 2: Window function

For databases that support window functions, a more efficient method can be used:

select x.username, x.date, x.value 
from (
    select username, date, value,
        row_number() over (partition by username order by date desc) as _rn
    from MyTable 
) x
where x._rn = 1

This method uses row numbers sorting on partition data, where the last date of each user is assigned a level 1.