Help with query.

Can anybody help with this query
SELECT
SUM(DBA.MAXBYTES)/1024 MAXSIZE,
(DBA.bytes - (NVL(SUM(free.bytes), 0))) / 1024 USEDSIZE
FROM
DBA_DATA_FILES DBA,
Dba_free_space free
WHERE DBA.TABLESPACE_NAME LIKE '%TAMMY%'

I get this error message.
ERROR at line 3:
ORA-00937: not a single-group group function
Thanks

You need a SQL course badly.

You are using aggreate/groupping function obviously you have to group your result set. You are querying two views and where is the join condition or you like cartesian products.... ???