SQL & PL/SQL

i'm using an employee table in which the phone number is stored as a character.. eg: 515.123.4567. i want to extract the last 8 numbers and convert it into a number format..

i user the following query..

select substr(phone_number,-8) from employees

and

select to_number(substr(phone_number,-8),'999.9999')*10000 Local_number from employees -- if i use this it says that ORA-01722 invalid number error..

but the following query

select to_number(substr(phone_number,-8),'999.9999')*10000 local_numbe from employees where department_id<=50 is working properly

but if i gve

select to_number(substr(phone_number,-8),'999.9999')*10000 local_numbe from employees where department_id<=150 --it throwing the same error, though dept 150 is nt thre in my table it should display the lesser, right?


'm using 9i database and in toad i executed these queries

regards renji