I have the following tables :

Table1 ( Col1 : varchar2, Col2 : number, Col3 : number)
Table2 ( Col1 : number, Col2 : varchar2, Col3 : varchar2)

I want to run a query like this :

select distinct Col2 from Table1 where Col1 in 
(
   select Col1 from Table2
)

Table1.Col1 is of type varchar2 while Table2.Col1 is of type number. so, I need to do some casting, it seems but it fails to succeed.

The problem is that any attempts to run the query returns the following error :

  ORA-01722: invalid number
  01722. 00000 -  "invalid number"
  *Cause:    
  *Action:

Table1.Col1 contains some null values.