Newbie: How to select from two dates and see the difference between allocated storage?

Hi,

I have  a table where we store the tablespace sizes each day. I would like to see how much the tablespaces have grown over 2012.

select tablespace_name, allocated from dbsnmp.TBS_SIZES_HISTORY where collection_Date= TO_DATE('1-1-2012','dd-mm-yyyy') order by 1;MINUSselect tablespace_name, allocated from dbsnmp.TBS_SIZES_HISTORY where collection_Date= TO_DATE('31-12-2012','dd-mm-yyyy') order by 1;

I get a value, but its not a "subtracted" value.

Well, that did not work. How do fix it?

Regards

S