Inserting 400 Million rows

 Hi,

I have a table table 1 and have the need to run the following to create the contents of table 2.

insert into t2 select a.col1, a.col2, b.col1, b.col2 from t1 a, t1 b

Table 1      

col1   col2

a         1

b          2

c         3

would result in

table 2

col1  col2  col3  col4

a       1       a       1

a       1       b       2

a       1      c         3

b       2      a         1

b       2       b       2

b       2        c       3

....  etc

The problem is my table 1 has 20,000 rows in it and the resulting table has 20k x 20k rows ... and it takes FOREVER .. if it finishes. 

What would be the best way to tackle this for time efficiency ???