How can i Calculate Transactions from DB

[Raju Boy]

I've developed a simple banking system containing Deposite and Withdraw.

I am using deposite,withdr aw and balance are my database fields

when i try to deposite the last balance fetched and then added with new deposite value i'm using (select last(deposite) from bank) this query to fetch last balance value .

sometimes the arrangement of database value changes so last(balance) value becomes wrong

how can i overcome this problem

if is there any technique to save transaction pls help me
thanking you in advance...

[Raju Boy]

if anyone an't understand my problem please inform i'll post briefly with all DB fields