Informix subqueries - how to execute them properly

Question

I'm working on an Informix query that wiil 1) Give me a list of call center agents and 2) give me their most recent status. I have a query that does almost everything I need;

select b.resourcename, b.extension, a.eventtype
from agentstatedetail as a, resource as b, team as c
where date (eventdatetime) = TODAY
  and (a.agentid = b.resourceid)
  and (b.assignedteamid = c.teamid)
  and (c.teamname like 'Team Name %')
group by b.resourcename, b.extension, a.eventtype
order by resourcename asc

However, this will give me a complete record of "eventtype" (eventtype shows the states an agent was in at a given time). I'm trying to pull only the most recent state. So, I believe I need to do a subquery to this main query stating something like, "If the main query's output is found in this subquery, then keep it". The subquery looks like this;

select a.agentid, b.resourcename, c.teamname, max(a.eventdatetime)
from agentstatedetail as a, resource as b, team as c
where date (eventdatetime) = TODAY
  and a.agentid = b.resourceid
  and b.assignedteamid = c.teamid
  and c.teamname like 'Team Name %'
group by a.agentid, b.resourcename, c.teamname

This subquery, by itself, is almost everything I need, but it doesn't have the eventtype. How would this query work?

This is the format that I typically write subqueries in but can't make work in Informix;

select a.agentid, b.resourcename, c.teamname, max(a.eventdatetime) as eventdatetime, a.eventtype from agentstatedetail as a, resource as b, team as c where date(eventdatetime) = TODAY and a.agentid=b.resourceid and b.assignedteamid=c.teamid and c.teamname like 'ITS %' and where a.eventdatetime in (select a.agentid, b.resourcename, c.teamname, max(a.eventdatetime) from agentstatedetail as a, resource as b, team as c where date(eventdatetime) = TODAY and a.agentid=b.resourceid and b.assignedteamid=c.teamid and c.teamname like 'Team Name %' group by a.agentid, b.resourcename, c.teamname) group by a.agentid, b.resourcename, c.teamname, a.eventtype order by max(a.eventdatetime) desc

Answer 1

Try doing an inner join with that subquery and agentstatedetail on agentid and the date that you found out that was the max:

select m.agentid, m.resourcename, m.teamname, a2.eventtype
from (
  select a.agentid,b.resourcename,c.teamname,max(a.eventdatetime) as maxtdate
  from agentstatedetail as a
  inner join resource as b on a.agentid = b.resourceid
  inner join team as c on b.assignedteamid = c.teamid
  where date (eventdatetime) = TODAY
    and c.teamname like 'Team Name %'
  group by a.agentid, b.resourcename, c.teamname
  ) m
inner join agentstatedetail a2 
    on a2.agentid = m.agentid and a2.eventdatetime = m.maxtdate

I'm a little confused on the columns that you want to see at the end. If these are not it, you will have to change them in the inner and outer queries.