Oracle-L: Re: SQL Query

From: Binley Lim <Binley.Lim_at_xtra.co.nz>
Date: Fri, 14 Nov 2003 20:29:25 -0800
Message-ID: <F001.005D6B44.20031114202925@fatcity.com>

Oh, right, #2 is refering to point-and-click GUI interfaces that some DBAs depend on that they no longer know how to write SQLs to navigate the data dictionary.

Original Message ----- From: Jared.Still_at_radisys.com To: Multiple recipients of list ORACLE-L Sent: Saturday, November 15, 2003 1:19 PM Subject: Re: SQL Query

Sorry, don't understand the DBA part ( #2 ).

       "Binley Lim" <Binley.Lim_at_xtra.co.nz> 
        Sent by: ml-errors_at_fatcity.com 
         11/14/2003 02:09 PM 
         Please respond to ORACLE-L 

               
                To:        Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> 
                cc:         
                Subject:        Re: SQL Query

Would have thought:

A developer would have known this - a SQL many-to-many join
A DBA would have known this - how else would you know what's happening with your tablespaces? (Clickety-pointy answers not allowed)
- Original Message ----- From: Jared.Still_at_radisys.com To: Multiple recipients of list ORACLE-L Sent: Saturday, November 15, 2003 9:54 AM Subject: Re: SQL Query

You can't join DBA_EXTENTS and DBA_DATA_FILES based on an equality of tablespace_name, and then add up the bytes of the files for the tablespace.

ie.

  select
    b.tablespace_name,
    b.bytes
  from dba_extents a, dba_data_files b
  where a.tablespace_name=b.tablespace_name

Try running that query, and it may become clear.

Your first query correctly aggregates the file sizes.

The second query determines tablespace size based on the number of extents allocated to it.

Drop all the objects in the tablespace, and your tablespace will no longer appear to have any space.

HTH Jared

       "Bellow, Bambi" <bbellow_at_chi.navtech.com> 
        Sent by: ml-errors_at_fatcity.com 
         11/14/2003 09:44 AM 
        Please respond to ORACLE-L 
               
               To:        Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> 
               cc:         
               Subject:        SQL Query

Friends --

Why would these two queries return different results?

This query works.

  SQL> l
  1 select
  a.tablespace_name,megs_allocated,megs_used,round(megs_used/b.megs_allocated,   2)*100 pct
  2 from (select tablespace_name,sum(bytes)/(1024*1024) megs_used   3 from dba_extents group by tablespace_name) a,   4 (select tablespace_name,sum(bytes)/(1024*1024) megs_allocated   5 from dba_data_files group by tablespace_name) b   6 where a.tablespace_name=b.tablespace_name   7* and a.tablespace_name='NAUAT'
  SQL> /

  TABLESPACE_NAME                MEGS_ALLOCATED  MEGS_USED        PCT
  ------------------------------ -------------- ---------- ----------
  NAUAT                                22924.25      11509         50

This query does not work

1 select a.tablespace_name,sum(b.bytes)/(1024*1024) megs_allocated, 2 sum(a.bytes)/(1024*1024) megs_used, 3 round(sum(a.bytes)/sum(b.bytes),4)*100 pct 4 from dba_extents a, dba_data_files b 5 where a.tablespace_name=b.tablespace_name 6 and a.tablespace_name='NAUAT'
7* group by a.tablespace_name,b.tablespace_name SQL> /

  TABLESPACE_NAME                MEGS_ALLOCATED  MEGS_USED        PCT
  ------------------------------ -------------- ---------- ----------
  NAUAT                              31773010.5      23018        .07

  Bambi.
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  Author: Bellow, Bambi
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Author: Binley Lim
INET: Binley.Lim_at_xtra.co.nz

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