Create Table Temp As Select * from Table

Question

What happens in the backend (performance point of view) when we create a table as follows:
Create Table Temp As Select * from Table1;
Suppose that the table Table1 has 10 million rows.
How is this different from inserting 10 million rows using Insert Statement in a script etc. into Temp table.
i.e. insert into temp values(1, 'description', sysdate);

Answer 1

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Create Table Temp As Select * from Table1; is always faster than inserting different rows using insert scripts.
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Incorrect - not sure where you got that information.
The two things being talked about that can affect performance are the use of direct-path loads and whether those loads are logged.
It makes no difference if the table is created first and then loaded using INSERT or if a CTAS is used to do both.
A traditional INSERT can use the APPEND hint to perform a direct-path load.
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Cretae table Temp As select * from Tabl1 does not generate logging to the database.Also as datatypes are determined automatically ,there is less work up front.
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The statement that CTAS 'does not generat logging' is incorrect. Whether logging is generated depends on whether the table is in LOGGING or NOLOGGING mode. A CTAS does not automatically, on its own bypass logging.
To bypass logging and existing table can be set to NOLOGGING mode
ALTER TABLE myTable NOLOGGINGAnd for CTAS the mode can be specified as part of the statement
Create table Temp NOLOGGING As select * from Tabl1;