Alter table to add primary key 6. Alter table to add primary key across more than one columns 6. Dropping a Column 6. New added columns are empty 6. Alter table to add unique with tablespace and storage setting 6.
Alter table to add primary key with tablespace and storage setting 6. Changing the Size of a Column. Oracle 11g introduced the concept of metadata-only default values. Queries of the new column were rewritten by the optimizer to make sure the result was consistent with the default definition.
Oracle 12c takes this a step further, allowing metadata-only default values of both mandatory and optional columns. Ricardo, April 21, - pm UTC. You can also catch regular content via Connor's blog and Chris's blog. Or if video is more your thing, check out Connor's latest video and Chris's latest video from their Youtube channels. And of course, keep up to date with AskTOM via the official twitter account. Questions Adding a column with a default value to a table.
Question and Answer. You Asked Tom, I have a doubt about adding columns with default values to a table. Thanks tom. April 21, - pm UTC. Sorry, not the same operations above, but with respect to the already existing values I meant.
A reader, September 15, - pm UTC. I've a partitioned table with size of 80G. Would alter table be better or add column, update value and add not null constraint? September 16, - am UTC. In 11g - fast add column, before that - it was a lock table, b add column, c update column, d commit.
A reader, September 16, - pm UTC. I should have mentioned its on 10g Thanks a bunch. Be careful when adding not-null columns with default values in 11g if you use triggers.
This is especially problematic if you use Designer-generated table APIs. They assign all column :new values to variables and back again. There is a bug that has been around since 11g, and still exists in If a variable is set to the :new.
Designer table APIs do this so you may get a "cannot insert null" error on a column you were not even updating. By the way, the workaround is to update every row, and set the new column equal to itself defeating the purpose of the fast add.
Cajie, December 30, - am UTC. Tom, The fast-add feature will certanily help improve the performance for large table, But, I have a doubt as far as the fast-add column is concern and would like to know how oracle handles this situtaions and displays result correctly. My question is how the oracle handles the different default values if they are being displayed at runtime?
December 30, - am UTC. I'm missing something here - like an insert or something??? And - when you insert new rows, they will have the default value right there in the row itself. Only pre-existing rows after you ADD a column use this new behavior.
Thanks Tom. Apologies Tom. There was a mistake in the script coz, I manually modified the script to explain the scenerio. I always try to write script as you do but everyone knows you are Tom and we only try to be Tom.
January 02, - am UTC. Tom, This is a very interesting feature. After reading this feature, I had the same question as the original poster: So my question is: Is it correct to assume what Arup Nanda says about Oracle getting the fact about the default value of the column at "query time" or Oracle still has to update all the rows when you specify a default value to a column and a not null constraint?
Can you please clarify? Does Oracle never actually update rows in the table and always gets the default value from data dictionary?
January 05, - am UTC. Arup is correct, and the entire point of this entire post is: with fast add column - when you add a column to a table and that column is NOT NULL with a default value - the table is not touched during the add column there is no locking there is no update the value will be supplied at retrieval time from the data dictionary.
Its close to what I would want. I would really like it if all "default" data were retrieved from the data dictionary and never actually persisted at the row level. But, that would come close to solving the "should it be NULL" vs "should I default something" arguments. January 05, - pm UTC. I would really like it if all "default" data were retrieved from the data dictionary and never actually persisted at the row level then you would never be able to change the default value - ever. As it is, you can change the default value after adding the column - because we will store the default value for any newly inserted rows.
We keep the default value of the column at the time of addition in the dictionary, but if it ever changes - we'll still keep it - but change the default value for any new rows added. This raises many more questions in my mind. Some are just "loud thoughts" which may be wrong. The tables in my mind are data warehouse tables.
Please let us know your expert opinion. In this column add scenario, for each row queried, Oracle will have to retrieve the value of the column from data dictionary. Would this lead to significant increase in IO against data dictionary? Oracle will also have to check if the value of the column for a given row is default or not. If it is default, return the data dictionary value otherwise return the actual value. Will this add some extra code path for each row?
This can also have impact on storage because there is no actual data stored in the column. If such a table is exported by conventional export though is it not recommended , will the column be exported null? I am assuming that data pump export would be smart enough to get the value from data dictionary.
Is there a way to override the behavior? It is part of the metadata for the table. No it won't. This will only apply to trailing null columns. Oracle simply stores the default expression exactly as you wrote it in the system catalog. SQL Developer simply displays that. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow.
Learn more. Asked 6 years, 3 months ago. Active 6 years, 3 months ago. Viewed 20k times. Improve this question. Do you have any reason for wanting this other than to satisfy your own curiosity? That's a valid reason, but other reasons might prompt other answers. Works just fine: sqlfiddle. What is the exact error message you get? Because the SQL client being used is irrelevant for the question.
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