SQL & PL/SQL

Hi


I need to compare account numbers from two different tables say a and b



I need to select the first four digits of account number from 'b' and match that with the first four digits in 'a'



for example in b if i have account number starting with 1234-----

I need to select all the account numbers from a which starts with 1234------ like 1234567,1234789etc.,


please help me out