Time Values Change When Creating a Wildcard Union from Text Files

Published: 05 Oct 2018
Last Modified Date: 11 Jan 2019


When creating a wildcard union of text files, time-only data values in the data set are converted to date-time values with the appending of the date "12-30-1899". This change also adds an AM/PM value to the time. There is no way to easily revert the data back to just the time values that were present in the underlying data.


  • Tableau Desktop 2018.1
  • Windows 10
  • Text Files with time-only string values in a column


This behaviort is currently by design.

There are three potential workarounds:

Option 1

  • Save the data in Excel and save it as an xlsx file instead, then the union will work as expected.​

Option 2

  • Create a calculated field using the DATEPART() function, which can be used to isolate the time portions of the field after the union. See the following documentation from our Online Help for more infomration: Date Functions

Option 3

  • Use manual unions rather than wildcard unions.


Tableau Desktop does not have a "time-only" data type. The time values in the data are therefore converted to the default "date-time" data type. This change is done automatically, when the wildcard union is compiled and the underlying time-only values are lost.
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