how to read Oracle blob data type using tableau

One workaround is to create a custom SQL that converts the field from Clob to Vchar then you can read it as normal text field here is an example os the SQL (the SUBSTR is important to trim the first 4000 characters of the blob, you get an error if the bolog is bigger than that, so that way we trim)

SELECT 

ID_BATCH ....AL YOUR FIELDS

,TO_CHAR(SUBSTR (BLOGF_FILED,1,4000)) AS MY_CLOBTEXTFIELD

FROM YOURTABL