Best way to clone a table?

Question

Hi,
What is the best way to clone an existing table definition?
What I mean is, I want to do the following:
create table tab2 as
select * from tab1;
delete from tab2;
commit;
But clearly this involves copying all the data and then delete it. Is there a more efficient way?
Another alternative I could think of is:
create table tab2 as
select * from tab1 where rownum < 2;
delete from tab2;
commit;
This would copy only one row instead of all the rows in tab1. This is clearly much more efficient than the first approach, but I still don't like the idea of copying the data and deleting it.
I am sure there would be a "cleaner" way. Any ideas?
Thanks in advance,
Rajesh

Answer 1

Hi Justin,
My work involves generating statistics by running various queries. So, I have written a few procedures that generate the statistics and insert into certain tables. Usually before starting to generate a new round of stats, I take back up of the previously generated data like this.
Approach I:
alter table summary_tab rename to summary_tab_20th;
create table summary_tab as
select * from summary_tab_20th
where rownum < 2;
delete from summary_tab;
commit;
Of course, another alternative I have is the following:
Approach II:
create table summary_tab_20th as
select * from summary_tab;
delete from summary_tab;
commit;
But I thought this is inefficient when compared to Approach I because it copies ALL the data from summary_tab to summary_tab_20th and then deletes ALL the data from summary_tab.
However, one disadvantage with Approach I is that everytime I do this the stored procedure gets invalidated and I have to recompile it.
So, that is where I stand. If all this looks very dirty, please suggest how I can 'clean up' my process :-)
Thanks,
Rajesh