How do I change the order before MySQL grouping?

Question

If there is more than 1 identical number in the table, I only bring one. But before bringing it, the first added date comes from the records. I want the last added record to come.

Here is an example;

SELECT * FROM comments WHERE phone_number='01234'

Output:

id | phone | created_at
-----------------------
1   01234   2020-10-27
2   01234   2020-10-28

MySQL code;

SELECT * FROM comments GROUP BY phone_number ORDER BY created_at DESC

MySQL output;

id | phone | created_at
-----------------------
1   01234   2020-10-27

Answer 1

If you want the most recent row, you don't want aggregation. Instead, filter for it:

select c.*
from c
where c.created_at = (select max(c2.created_at)
                      from comments c2
                      where c2.phone = c.phone
                     );

Or use window functions:

select c.*
from (select c.*,
             row_number() over (partition by phone order by created_at desc) as seqnum
      from comments c
     ) c
where seqnum = 1;

Or, if you want this just for one phone, then you can use order by and limit:

select c.*
from c
where phone = '3244003390'
order by c.created_at desc
limit 1;