Retain values till there is a change in value in Teradata

Question

There is a transaction history table in teradata where balance gets changed only when there is a transaction Data as below:

Cust_id Balance Txn_dt
123     1         


        

Answer 1

There are several ways to get this result, the simplest in Teradata utilizes Time Series Expansion for Periods:

WITH cte AS
 (
   SELECT Cust_id, Balance, Txn_dt,
      -- return the next row's date
      Coalesce(Min(Txn_dt)
               Over (PARTITION BY Cust_id 
                     ORDER BY Txn_dt
                     ROWS BETWEEN 1 Following AND 1 Following)
              ,Txn_dt+1) AS next_Txn_dt
   FROM tab
 ) 
SELECT Cust_id, Balance
  ,Last(pd) -- last day of the period
FROM cte
-- make a period of the current and next row's date
-- and return one row per day
EXPAND ON PERIOD(Txn_dt, next_Txn_dt) AS pd

If you run TD16.10+ you can replace the MIN OVER with a simplified LEAD:

Lead(Txn_dt)
Over (PARTITION BY Cust_id 
      ORDER BY Txn_dt)