What is the right way to process table (1000000 rows) row-by-row

Question

Hi all,
Please suggest me what will be best way to processing 1000000 records  in following logic..

Begin Loop on Master Table
   Posting on Transaction File
   Begin Loop on Detail Table
      Posting on Transaction File   
   Loop
Loop
---------------------------------------------------
Posting Procedure on Transaction File
If record not exits in Transaction File
   Begin
      Insert New Record
   End
Else
  Begin
    Update Same records
  End

- Regrds
A Roy Chowdhury