How can I conditionally fill down/flash fill NULL values with previous values based on certain criteria?

Hi @KCMT,

thanks for your question!

There’s several ways you can achieve the fill down (or “fill forward” or “last non empty”) - four of them are described here:

https://www.andrewvillazon.com/forward-fill-values-t-sql

The most transparent and concise way to achieve this is the LAST_VALUE/FIRST_VALUE functions of T-SQL: https://learn.microsoft.com/en-us/sql/t-sql/functions/last-value-transact-sql?view=sql-server-ver16

SELECT 
    FIRST_VALUE( [CardCode DUAL] ) OVER (
        PARTITION BY [company key], [project]
        ORDER BY some_timestamp_or_id
        ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
    ) AS CardCode_DUAL_FILLED_FORWARD,

    FIRST_VALUE( [Route Bron] ) OVER (
        PARTITION BY [company key], [project]
        ORDER BY some_timestamp_or_id
        ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
    ) AS Route_Bron_FILLED_FORWARD

FROM [actual_table]

Within TimeXtender you would create a custom view that has the filled-forward columns, and then update the actual table from that view.

Please let us know if that info helps you taking the next steps.