Want to make the sql insert run faster

Question

Hi,
Need a small advice to make an insert statement of 7 million run faster.Currently taking 30min +.What is the difference between the following methods?which is the best method to adopt?
1)Drop Table Single
2)Create Table Single NoLogging
As
Select * From table1
Union All
Select * From table2
Union All
Select * From table3
Union All
3)Enable Constraints
or
1)Truncate table
2)disable constraints
3)INSERT /*+ APPEND */
INTO table
Select * From table1
Union All
Select * From table2
Union All
Select * From table3
Union All
4) Enable constraints
Thanks

Answer 1

Hi,
>>What is the difference between the following methods?
As far as I know direct-path load will bypass the buffer cache and will write directly to blocks within the tables you are loading. I'm no sure about CTAS method ...
SQL> alter system flush shared_pool;
System altered.
SQL> alter system flush buffer_cache;
System altered.
SQL> set timing on
SQL> create table tt1 nologging as select table_name from dba_tables;
Table created.
Elapsed: 00:00:36.59
SQL> truncate table tt1;
Table truncated.
Elapsed: 00:00:00.23
SQL> alter system flush shared_pool;
System altered.
Elapsed: 00:00:00.04
SQL> alter system flush buffer_cache;
System altered.
Elapsed: 00:00:00.54
SQL> insert /* +APPEND */ into tt1 nologging select table_name from dba_tables;
23480 rows created.
Elapsed: 00:00:02.89Cheers
Legatti