I think you are not getting a response because you are not very clear on what you want to do. But if you are trying to split the input rows into two groups at random on a 25%, 75% split then the following will do that. Not sure that is what you want.
select * from u1 order by 1;
*** Query completed. 10 rows found. 2 columns returned. *** Total elapsed time was 1 second.