Simple Query with subquery returns the 'wrong' result

Question

DB version: 11.2
We created about 27 schemas in the last 4 days. The below query confirms that.
SQL > select username, created from dba_users where created > sysdate-4;
USERNAME                       CREATED
MANHSMPTOM_DEV_01              12 Jul 2012 11:55:16
PRSM01_OAT_IAU                 13 Jul 2012 01:51:03
F_SW                           11 Jul 2012 17:52:42
FUN_CDD_HK_SIT                 09 Jul 2012 15:33:57
CEMSCOMPTOM_UAT_01             12 Jul 2012 11:43:45
STORM02_OAT_IAU                13 Jul 2012 02:06:29
27 rows selected.  -------------> Truncated outputFrom DBA_TS_QUOTAS.max_bytes column , we can determine the space quota allocated for a user/schema
SQL > desc dba_ts_quotas
Name                                      Null?    Type
TABLESPACE_NAME                           NOT NULL VARCHAR2(30)
USERNAME                                  NOT NULL VARCHAR2(30)
BYTES                                              NUMBER
MAX_BYTES                                          NUMBER
BLOCKS                                             NUMBER
MAX_BLOCKS                                         NUMBER
DROPPED                                            VARCHAR2(3)So, I wanted to see the allocated space for the users created in the last 4 days. The below query should return only 27 records because the subquery returns only 27 records. Instead it returned 66 records !
select username, tablespace_name, max_bytes/1024/1024 quotaInMB
from dba_ts_quotas
where username in (select username from dba_users where created > sysdate-4);Any idea why ? I know it is not a bug with oracle. Its just I haven't been eating fish lately.

Answer 1

Hi,
J.Kiechle wrote:
So, I wanted to see the allocated space for the users created in the last 4 days.DBA_TS_QUOTAS doesn't give the allocated space but rather the maximum allowed for a given user.
J.Kiechle wrote:
The below query should return only 27 records because the subquery returns only 27 records. Instead it returned 66 records !What if your user John has Quotas on 3 tablespace TBS1, TBS2 and TBS3 ?
You cannot expect the outer query to only retrieve at most 27 rows just because the inner query returns 27 rows.
For allocated space by tablespace for recently created users, you'd better query dba_segments. something like :select owner, tablespace_name, trunc(sum(bytes)/1024/1024) alloc_mb
from dba_segments
where owner in (select username from dba_users where created > sysdate - 4)
group by owner, tablespace_name
order by owner, tablespace_name;