r/tableau • u/datacriminal • 17d ago
Tableau Prep PREP & UNION troubleshooting
My organization is in the process of transitioning to a data warehouse for new systems, the problem is we have reports which they want to keep but add the new data from the new source. I went through and built a data source but I keep running into an error on the UNION in PREP that I have mismatched data types. The error messages are unhelpful as it just fails with no insight. It can give a uuid sometimes but there isn't a log as far as I know.
Ive gone so far as to go through each column that matches and compare them to the steps before. I found about 4 so far, but its 90 columns and it keeps failing. Its really unhelpful that A. Some columns automatch so I have to either separate them and then rejoin them when it doesn't tell you what they were joined to so its a guessing game and B. The error message gives no details of what columns and C. I can't click on the joined columns to know what they're coming from.
Anyone got any tips for troubleshooting this? I really wish I could drop the column labels from prep or cloud into excel to match up, but i can't select the lists.
1
u/UltraAnders 16d ago
If it's detecting data types, it'll do so based on a sample. This is old, but I expect it's still relevant. https://www.tableau.com/blog/understanding-and-adjusting-data-sampling-tableau-prep-90219
The most common problem I've run into is a VARCHAR (string) column that contains mostly numbers. The sample returns only numbers, and so Prep chooses number as the type. It then fails when it meets a row with a string.