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Oracle Tips by Burleson 

Using CTAS with an Index Hint

The CTAS with an index hint executes quite differently than CTAS with order by. When using an index hint, the CTAS begins by retrieving the table rows from the original table using the existing index. Since the rows are initially retrieved in the proper order, there is no need to sort the result set, and the data is used immediately to create the new table.

The syntax for CTAS with an index hint appears below:
create table new_customer
tablespace customer_flip
storage (initial 500m
next 50m
maxextents unlimited)
as select /*+ index(customer customer_primary_key_idx) */ *
from customer;


When this statement executes, the database traverses the existing primary-key index to access the rows for the new table, bypassing the sorting operation. Most Oracle DBAs choose this method over the order by approach because the runtime performance of traversing an index is generally faster than using the PARALLEL clause and then sorting the entire result set.


The above is an excerpt from the "Oracle9i UNIX Administration Handbook" by Oracle press, authored by Donald K. Burleson.

 

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