sayan wrote:
NVL(colname,old_col)
which is brilliant, especially if you have time based partitioning and eventual
“unhook partition” purging at some age (like the common 7 years or 25 years for
EPA projects). At some point then, no values would exist in old_col and you
could drop the wrapper, without ever copying squat, since all your new values
go into the “new” colname without changing a line of code.
mwf
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Sayan Malakshinov
Sent: Monday, March 22, 2021 7:44 AM
To: Lok P
Cc: ahmed.fikri@xxxxxxxxxxx; oracle list
Subject: Re: Re: Column Length modification
Hi Lok,
I would prefer Jonathan's approach or renaming old column and creating new one
with the same name, but with new precision and wrapper view with
NVL(colname,old_col).
But if you really want to change it, I would change your approach: instead of
p.1 "create backup table using CTAS", I would create partitioned table
backup_table and use "alter table backup_table switch partition with old_table".
It will make an original table empty, so you don't need p.2.
On Mon, Mar 22, 2021 at 2:25 PM Lok P <loknath.73@xxxxxxxxx> wrote:
Thank You So much. So just to avoid missing any grants synonyms and related
consequences like invalidation of package/procedure etc. Is it good to just
intact the main table but move data in and out , something as below..
1)Create a backup table as "tab1_backup" from the main table TAB1 using CTAS
approach using parallelism without creating indexes constraints etc on the
backup table.
2)Truncate the main table TAB1.
3)make the indexes UNUSABLE in the main table TAB1.
4)Alter the column in the main table TAB1 to modify the existing column from
number(15,5) to number(22,0).
5)Insert data into the main table(tab1) from the backup table(tab1_backup)
using direct path load + parallel threads. And in case of unusable indexes this
step should be pretty fast.
6)Rebuild the indexes in the main table.
Regards
Lok
On Mon, Mar 22, 2021 at 4:16 PM ahmed.fikri@xxxxxxxxxxx
<ahmed.fikri@xxxxxxxxxxx> wrote:
oracle does the same when you add the new colum, update it and remove the old
one (so doing this, the table is recreated three times).
just use direct load + parallel + constraints novalidate. This work perfectly
even for huge tables
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--- Original-Nachricht ---
Von: Lok P
Betreff: Re: Column Length modification
Datum: 22. März 2021, 11:38
An: Jonathan Lewis
Cc: Oracle L
Just that, i think the option of creating the new object fully with the data
and rename afterwards by dropping the original object may not be a good option
if the object which we are trying to alter is in TB's and partitioned, thinking
if any other possible way to achieve the same?
On Sun, Mar 21, 2021 at 8:09 AM Lok P <loknath.73@xxxxxxxxx> wrote:
Thank you Jonathan.
Yes it's exactly the same error ORA-01440: which we are encountering. And the
column is not having any data with non zero precision. But as we are
standardizing the data elements across our applications, we want to now not
allow any junks in future and thus trying to fix the precision thing as part of
this length modification. This will make things consistent across all our
applications and easy for understanding.
Now if my understanding is correct, the way you are suggesting i..e altering
column length as (22,7) (which will not make any ORA-01440 error happen )+
having the check constraint added to the table will technically help us
achieving the same thing (without any additional performance overhead) as
simply altering the length to number(22,0). But is it something that will
create confusion and thus we should keep it clean i.e. column length (22,0)
only without any additional constraint? And to achieve that , is the best
approach is the one suggested by Ahmed i.e. create the object fully with the
new structure(i.e. with number(22,0)) and then drop the old one and rename the
new one?
Regards
Lok
On Sun, Mar 21, 2021 at 3:30 AM Jonathan Lewis <jlewisoracle@xxxxxxxxx> wrote:
If you're see an error then show us exactly what it is.
I assume it's
ORA-01440: column to be modified must be empty to decrease precision or scale
You're trying to change a column from (15,5) to (22,0) which means you're going
to lose 5 decimal places - do any of the rows have data that isn't purely
integer, if not are you happy for the values to change as you go from 5d.p. to
integer?
If you need 22 digits precision, and no decimal places you could modify your
column to (27,5) and then add a check constraint that says (check colX =
trunc(colX)) as a way of ensuring that you don't have any non-integer values.
(You could update the table,set colX to trunc(colX) where colX !=
trunc(colX)before adding the constraint, or you could add the constraint
enabled but not validated, then do the update then set the constraint
validated. ** or ceiling() or round(), depending on what you think best suits
your requirements
Regards
Jonathan Lewis
On Sat, 20 Mar 2021 at 19:10, Lok P <loknath.73@xxxxxxxxx> wrote:
We are using version 11.2.0.4 of Oracle exadata. Our requirement is to modify
column length of a table from Number(15,5) to Number(22) and we are seeing
errors and its saying to make the column empty before making this modification.
So to achieve this we are thinking of doing this in multiple steps like
1) Add new column(COL_new) with number(22,0) to the same table
2)Then update the new column with all the values of original column(say COL1)
3)Then drop the original column(COL1) which is having length number(15,5)
4)Then rename the new column(COL_NEW) to original i.e. COL1.
We are in the process of doing multiple such modifications to some big
partition and non partitioned table. And in this process the Update seems to be
a tedious one as it will scan the full table and may lead to row chaining and
also drop the existing column and renaming new columns will need the
application to stop pointing to this object or else they may fail. Also stats
seems to be gathered fully again on the table after this along with if any
index pointing to these columns needs to be recreated. So multiple issues
highlighted with this process by the team. Want to understand from experts if
there exists any better way of achieving this with minimal interruption and in
quick time?
Thanks
Lok
--
Best regards,
Sayan Malakshinov
Oracle performance tuning engineer
Oracle ACE Associate
http://orasql.org
