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So i've been searching all around on how i could increment a column in Teradata. I'm new to this so im not really familiar with all the syntax or tactics that i could use. 
I've read about autogenerated identity column, OLAP and recursive in teradata but i think it does not matches my need. 
So here's my problem.

I am trying to load a very wide file into a Teradata table using BTEQ and unfortunately the records do not have a unique identifier other than record number which is implied by their location in the file (ie.

I have a table with Columns A, B below but I want to create Column C

Column C is explained as follows: Ordering by Column A ASC I want to replicate the value od Column B for all succeeding rows until a Non-Null value is met, then start again.


I just want to know is there a way to update a table based on the rowid.
Lets say I have custid in tableA and Cust Id in TableB , I want to bring all the custid of tableB into TableA based on the ROWID.