Blending will result in duplication of records also limits the functionality available to you in tableau
if you MUST blend you need to consider which values come from the primary source (they are not aggregate in a calculation) and which come from the secondary ( they are aggregate as you bring them into the primary source) and account for that in the formulas you create
try to create a join that results in a single combined data set - without seeing the twbx workbook and understanding the data structures it is difficult to be of much help
in general joining will allow you to extend the dimension (Number of column) - just have to think through what you want in the result
e.g. if you are pulling data from an erp system and you have all you sales data and you want to pull in data from the material master you would join on the Product ID
If you can share the workbook - even with dummy data we can be more specific
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