Finding row of "duplicate" data with greatest value

Question

I have a table setup as follows:

Key || Code || Date
5       2      2018
5       1      2017
8       1      2018
8       2      2017

I need to retrieve only the key and code where:

Code=2 AND Date > the other record's date

So based on this data above, I need to retrieve:

Key 5 with code=2

Key 8 does not meet the criteria since code 2's date is lower than code 1's date

I tried joining the table on itself but this returned incorrect data

Select key,code 
from data d1
Join data d2 on d1.key = d2.key
Where d1.code = 2 and d1.date > d2.date

This method returned data with incorrect values and wrong data.

Answer 1

Perhaps you want this:

select d.*
from data d
where d.code = 2 and
      d.date > (select d2.date
                from data d2
                where d2.key = d.key and d2.code = 1
               );

If you just want the key, I would go for aggregation:

select d.key
from data d
group by d.key
having max(case when d2.code = 2 then date end) > max(case when d2.code <> 2 then date end);