Select most recent row with GROUP BY in MySQL

Question

I\'m trying to select each user with their most recent payment. The query I have now selects the users first payment. I.e. if a user has made two payments and the paym

Answer 1

I read the following solution on SO long ago, but I can't find the link to credit, but here goes:

SELECT users.*, payments.method, payments.id AS payment_id, payments2.id
FROM users
JOIN payments
    ON users.id = payments.user_id 
LEFT JOIN payments2
    ON payments.user_id = payments2.user_id
    AND payments.id < payments2.id
WHERE payments2.id IS NULL

To understand how this works, just drop the WHERE payments2.id IS NULL and you'll see what is happening, for instance it could produce the following output (I haven't build the schema to test this, so it's pseudo-output). Assume there are the following records in payments:

id | user_id | method
1  | 1       | VISA
2  | 1       | VISA
3  | 1       | VISA
4  | 1       | VISA

And the above SQL (without the WHERE payments2.id IS NULL clause) should produce:

users.id | payments.method | payments.id | payments2.id
1        | VISA            | 1           | 2
1        | VISA            | 1           | 3
1        | VISA            | 1           | 4
1        | VISA            | 2           | 3
1        | VISA            | 2           | 4
1        | VISA            | 3           | 4
1        | VISA            | 4           | NULL

As you can see the the last line produces the desired result, and since there's no payments2.id > 4, the LEFT JOIN results in a payments2.id = NULL.

I've found this solution to be much faster (from my early tests) than the accepted answer.

Using a different schema but a similar query, of 16095 records:

select as1.*, as2.id
from allocation_status as1
left join allocation_status as2 
    on as1.allocation_id = as2.allocation_id
    and as1.id < as2.id
where as2.id is null;

16095 rows affected, taking 4.1ms

Compared to the accepted answer of MAX / subquery:

SELECT as1.* 
FROM allocation_status as1
JOIN (
    SELECT max(id) as id
    FROM allocation_status
    group by allocation_id
) as_max on as1.id = as_max.id 

16095 rows affected, taking 14.8ms