Get last distinct set of records

Question

I have a database table containing the following columns:

id   code   value   datetime   timestamp

In this table the only unique values res

Answer 1

I'll try something like this :

select * from table
where id in (
    select id
    from table
    group by code
    having datetime = max(datetime)
)

(disclaimer: this is not tested)

If the row with the bigger datetime also have the bigger id, the solution proposed by smdrager is quicker.