date        val  summa
 01 / 01 / 2011 , USD,  5000 
 01 / 01 / 2011 , EUR,  7000 
 02 / 01 / 2011 , USD,  3000 
 02 / 01 / 2011 , USD,  3000 
 03 / 01 / 2011 , USD,  1000 
и т.д.

date       val curs
 01 / 01 / 2011 ,USD, 30 
 02 / 01 / 2011 ,USD, 31 
 04 / 01 / 2011 ,USD, 30 

select T.date, T.val, T.summa,valcurs.curs, T.summa*valcurs.curs as rubsumma
from
	(
	select zatr.date, zatr.val, zatr.summa, max(valcurs.date) as maxdate
	from zatr 
	left join valcurs on (zatr.val=valcurs.val and zatr.date>=valcurs.date)
	group by zatr.date, zatr.val, zatr.summa
	) as T
inner join valcurs on (T.val=valcurs.val and T.maxdate=valcurs.date)

select u.date, u.val, u.summa, u.curs, u.rubsumma,u.maxdate,
	val_cur.curs as cursUsd, u.rubsumma/val_cur.curs as usdsumma
from 
	(select R.date, R.summa,r.curs, R.val , max(val_cur.date) as maxdate,r.rubsumma 
	from 
		(select T.date, T.val,T.summa,val_cur.curs as curs, T.summa*val_cur.curs as rubsumma
		from
			(select zatr0.date, zatr0.val, zatr0.summa, max(val_cur.date) as maxdate
			from 
				(select date, sum(summa) as summa,val 
				from zatr  
				where date>='2011-01-01' and date<='2011-28-02'	
				group by date,val) as zatr0
				left join VAL_CUR on (zatr0.val=VAL_CUR.val and zatr0.date>=val_cur.date)
				group by zatr0.date, zatr0.val, zatr0.summa
			) as T
			inner join val_cur on (T.val=val_cur.val and T.maxdate=val_cur.date)
		) as R
		left join VAL_CUR on (R.date>=val_cur.date and val_cur.VAL= 3 )
	group by R.date, R.val, R.summa
	) as u
inner join val_cur on ( 3 =val_cur.val and u.maxdate=val_cur.date)