Update Multi File

Hi,
I have the following case:-

File a(transaction File)__File b(summary File)___File c(summary)
acctno___Value DB/CR_____Acctno DB,CR_______acctno DB,CR
1___________100db___________1______________________1
1___________300cr___________2______________________2
1___________600db
2___________700db

I want to update the account on table b and c from table a.

My current update is just for one table as follows:-
UPDATE amaster
SET cmdb = cmdb +
(SELECT SUM(transact.damt) AS Expr1
FROM transact
WHERE (acctno = amaster.acctno)
GROUP BY acctno),
cmcr = cmcr +
(SELECT SUM(transact.camt) AS Expr1
FROM transact
WHERE (acctno = amaster.acctno)
GROUP BY acctno)
FROM amaster INNER JOIN
transact ON transact.acctno = amaster.acctno



thanks