On Oct 26, 2012, at 5:24, Gary Stainburn <gary.stainburn@ringways.co.uk> wrote:
> This is my best effort so far is below. My concern is that it isn't very
> efficient and will slow down as record numbers increase
>
> create view current_qualifications as
> select q.*, (q.qu_qualified+q.qu_renewal)::date as qu_expires from
> qualifications q
> join (select st_id, sk_id, max(qu_qualified) as qu_qualified from
> qualifications group by st_id, sk_id) s
> on q.st_id=s.st_id and q.sk_id = s.sk_id and q.qu_qualified = s.qu_qualified;
>
>
> select t.st_id, t.st_name, k.sk_id, k.sk_desc, q.qu_qualified, q.qu_renewal,
> q.qu_expires
> from current_qualifications q
> join staff t on t.st_id = q.st_id
> join skills k on k.sk_id = q.sk_id;
>
The best way to deal with recency problems is to maintain a table that contains only the most recent records using
insert/update/deletetriggers. A boolean flag along with a partial index can work instead of an actual table in some
cases. If using a table only the pkid needs to be stored, along with any desired metadata.
It probably isn't worth the effort until you actually do encounter performance problems.
David J.