Via the Unions tab, you can create a new dimension based on many-to-many relationships between the columns of different tables. You can use this option to create a dimension, for example, by unifying the product columns of two tables.
Click the Unions tab to define unified dimensions.
To create a unified dimension:
1. Click Add 
.
2. Enter a Title for the new dimension.
3. In Table, select the tables whose columns you want to unify.
4. In the Fields Mapping area, choose the columns you want to map. To add more column mappings, click the Add 
button.
Select the key check box to designate a mapping as the key.
5. Click Apply.