I have three tables in an Access database that I'm plugging into tableau.
1) Sales table: has about 1.5M rows of data, the key fields being the day of sale and the item code.
2) Item reference table: has around 50K rows and contains information pertaining to that item, the key field being Item Name
3) Access Query: Sometimes the Item doesn't have a name, so I have a query that uses a DLOOKUP to find a replacement.
OK, so in Access it all looks good. I then join the Sales table to the Query using the Item Code, so every Sale has an Item Name even if that Item code doesn't have a name in the reference table. All going well.
And when I build tables in tableau everything works. (Go me! I'm so clever blah blah blah). However, when I create an extract and have the "use extract" box ticked, all of a sudden only about 5% of the joins seem so work and my sales are split between the correct name, and a null value.....?????
When I uncheck Use Extract, the query running box appears, runs for 30 secs or so, then the full data is back and all Sales are back against the item name....
I have no idea what's going on. Anyone come across this problem before???