No Alert For Data Type Mismatch Results In Null Values

Published: 04 Mar 2021
Last Modified Date: 27 Oct 2022


When using a text or excel based data source Tableau samples the top data in each column and makes its best effort to assign a data type to the column that will avoid errors.

For example:

If most rows in the sampled column are numbers but some are strings, Tableau will set the field as a string because numbers can exist in string fields, but strings cannot exist in number fields without error. However if all of the rows in the sampled data are numbers and Tableau assigns the number data type, any non-number value like a string encountered in the field get handled by tableau usually by setting the value to null as described here: Mixed data types in data from files
  • This behavior can result in users seeing unexpected total values as well as differences between the source data file and what appears in the tableau visualization unless the user notices the data type Tableau has assigned is incorrect for their use and makes a change manually to the data type.


  • Tableau Desktop
  • Tableau Server (Web Edit)


Workaround Options:
  • Clean the data source files to contain a consistent data type (string, number, date, etc.) in each column prior to connecting the data to Tableau.
  • Check data types after connecting data to ensure desired type is selected for each field in Tableau.


The ability for Tableau to alert a user when a data type mismatch results in a null value is not currently built into Tableau products.
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