Question

I have a table like this:

ID    Type   UserID    Timestamp    
1     1      1000      1312389223
2     1      1000      1312389220
3     2      1000      1312389215
4     3      1000      1312389213
5     3      2000      1312389205
6     1      2000      1312389201
7     2      1000      1312389190

What I need now, is to retrieve only certain parts of the data in this table. The list shows data in relation to what a certain user has been doing on my site.
Some of the “Type”‘s need to have all entries shown. Others need only to have the most recent shown.

In the above example I need to have all occurances of Type = 2 shown, but only top 1 (ordered by Timestamp) of Type = 1 shown. Same goes for Type = 3. This is per UserID basis.

Hope I have explained myself clear enough.

Thanks in advance for your help,
fischer.

Answer 1

Simple and quick solution if you dont need IDs

select user, type, timestamp from Table where type = 2
union
select user, type, max(timestamp) from Table where type in (1,3) group by user, type

That will keep IDs, but it’s more complicated and somewhat slower:

select * from Table where type = 2
union
select * 
from Table t
join (
    select type, user, max(timestamp) as timestamp
    from Table 
    where type in (1,3)
    group by type, user
) tt on tt.user = t.user and tt.type=t.type and tt.timestamp = t.timestamp

Anyway, both solutions are not very scalable