SQL - 与同一列中的多个值进行比较？

Question

Ok, so I'm trying to write some SQL and I'm not sure how to tackle this situation. I have a table similiar to what is below. The basic idea is that I need to get the records that are in an 'H' status (easy enough), but I need to exclude records that were in an 'H' status and moved on to an 'A' status at a later date.

So ideally, the results should only return the last two records, IDs 03 and 04. How would you guys do this?

ID     STATUS     STAT_DATE
01       A        05/01/2013
01       H        05/01/2012
02       A        12/01/2013
02       H        12/01/2012
03       H        03/01/2009
04       H        02/01/2008

Answer 1

You could do it this way:

select *
from t t1
where status='H' and not exists(
    select * 
    from t t2 
    where t1.id=t2.id and t2.status='A' and t2.stat_date > t1.stat_date)

That will give you all entries of table t with status='H' where there is no entry in t with the same id, a later date, and status='A'.