Count Distinct (COUNTD) is a function that counts the unique values in a measure or dimension. This function is not available for data sources that use a live connection to Microsoft Access, Microsoft Excel, and text files.
Possible errors are COUNTD function missing and Unknown function COUNTD called
The Microsoft JET database engine used to access these types of data sources does not support the Count Distinct function.
This function is supported by the Tableau Data engine. To change the data connection to use the Tableau Data engine, please take a data extract.
To create a data extract:
Step 1
Select Data > Extract Data.
Step 2
Click the Extract button, and then save your extract.