The best choice would be to let the database do it for you. Consequently, I agree with my predecessors, that this is merely a sql related problem.

The join

select
  <do sth useful here>
from 
table a
inner join
table b
on
a.date<b.date
inner join
table c
on b.date<c.date
[download]

(and so on) will do it for you.

Because your tables are small it should be quite fast. An iterative perl solution would be possibly less efficient, not to mention the required connection overhead. If you have to do it regularly create a view. In case your database has a join problem google for 'correlated subqueries'.

I use perl in such circumstances for automatic creation of these annoying statments.