KNOWLEDGE BASE

Using ISNULL() In The Calculated Field To Apply Cleaning Process May Significantly Delay The Flow Preview Display in Tableau Prep


Published: 01 Jun 2021
Last Modified Date: 01 Jun 2021

Issue

Heavy use of ISNULL() in nested calculations of calculated fields to apply cleaning operations could cause significant delays in the flow preview display in Tableau Prep.
 

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    Environment

    • Tableau Prep Builder & Prep Conductor
    • Tableau Online
    • Tableau Server

    Resolution

    Workaround:
    If the original data contains a large number of NULL values, please consider using a DB-side function (such as custom SQL) to replace the fixed dummy values before filtering the data.

    Cause

    Filter by calculation is useful for filtering out certain characters or values, but replacing a fixed dummy value for every null value can be very "expensive". 
    When in interactive mode, the more ISNULL functions and IF statements you bring into Prep Builder, the more the flow will be computed. While there are no limitations on using functions in the Prep Builder, but there are considerations to optimize performance.

    Additional Information


     
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