question about long running query with membership condition "in (...)"

We are running oracle 8.17 on sunos 5.8

Can anyone please explain why when I run the following individual queries they run for 1 second, but when I combine them, it runs forever.

INDIVIDUAL QUERIES:  select SUM(bytes),

     tablespace_name
    from sys.dba_free_space where tablespace_name in ('PTA')     group by tablespace_name;

 select SUM(bytes),

     tablespace_name
    from sys.dba_free_space where tablespace_name in ('ILIS')     group by tablespace_name;

COMBINED QUERY:  select SUM(bytes),

     tablespace_name
    from sys.dba_free_space where tablespace_name in ('PTA' ,'ILIS')     group by tablespace_name;

Thank you very much. Received on Thu Feb 05 2004 - 10:39:41 CST