Breaking down values in a large table

Listers,
I have a table of 125M rows (not partitioned) which I am exporting. I want to break the export into 4 dmp files using the query command on the pk column.  

I am looking at how the best way of finding the values of the PK (number) which are at 25%, 50% and 75% ish for the table so that I can get 4 evenly sized exports  

My query line in the parameter file will be along the lines of where

1)       log_no < xx
2)       log_no >= xx and < yy
3)       log_no >= yy and < zz
4)       log_no >= zz
 

I am thinking of a sql something like the following  

Select /*+ index ffs(table_name index_name) */ Log_no , floor(log_no / 4), count(*)
>From table_name group by floor(log_no / 4), log_no
 

Version is 8.1.7.1  

Can anybody help please  

Thanks  

John    

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Author: John Hallas
  INET: john.hallas_at_hcresources.co.uk

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