Question

I need to create a table from another table but I only want the last 10000 records to be added in the new table. Can any one tell me how this can be done by modifying this statement:

create table export_cluster_125m
as
(select * from cluster_125m);

Answer 1

You say you want the “last” 10000 rows. Assuming this can be determined by a column such as created_date you would need to order by that column (descending) and then take the first 10000 rows returned by that query. This can be done using ROWNUM, but not like this:

-- Will not work correctly
select * from cluster_125m
where rownum <= 10000
order by created_date desc;

That will return some 10000 rows, ordered by created_date (descending) – but they will not generally be the latest 10000 rows. To do that you need to nest the query like this:

select * from
( select * from cluster_125m
  order by created_date desc
)
where rownum <= 10000;

Now all rows are sorted in descending order, and then the first 10000 are taken.