Why does INSERT ... AS SELECT ... use TEMP, contrary to CREATE TABLE ... AS SELECT...?

Oracle 9.2.0.5.0 on Open VMS Itanium.

I have a table SRC with degree default, and parallel dml enabled for the session. If I do:

CREATE TABLE tgt
PARALLEL NOLOGGING
AS SELECT * FROM src

data from SRC is read, and written immediately to TGT, in 4-fold parallel.

If I then truncate table TGT, and do a

INSERT INTO tgt
SELECT * FROM src

data from SRC is read into temporary tablespace buffers first, and after that the buffer contents is written to TGT, again all in 4-fold parallel.

Why the detour in case of the INSERT?

Regards, Jaap. Received on Sat Jan 13 2007 - 04:02:47 CST