about oracle sql injection

hey i need little help,when i try to inject commands into an oracle database 
example:

union select password from dba_users--

gives the error message

:ORA-***: query block has incorrect number of result columns 

i then cycle through different amount of column numbers until i get to 
something like:

UNION SELECT 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22 from 
dba_users--

which produces the error:

ORA-***: expression must have same datatype as corresponding expression 

1)Does anyone know a quick way to get all the column types without cycling 
through manually as that will take 2^22 requests atleast?

2)Is there anyway to get information out of the db without knowing the column 
types?

thanks alot

limor