Comprehensive and Detailed Explanation From Exact Extract:
To combine Excel and SQL Server data in the same logical data model, Tableau offers two supported capabilities:
Relationships
* Recommended modern method for combining tables from multiple sources.
* Supports cross-database relationships between Excel and SQL Server.
* Maintains separate physical layers but integrates data at query time.
Cross-Database Joins
* Allows joining data from different databases in the physical layer.
* Fully supported for Excel + MS SQL Server.
* Useful when granular row-level merging is needed.
Why the other options are incorrect:
C). Data Blending
* Legacy feature, used only when no direct combination is possible.
* Tableau recommends relationships instead.
* Produces separate queries and may lose row-level detail.
D). Union
* Requires tables to have equivalent structure.
* Cannot union Excel with SQL Server unless identical column structure exists.
* Not appropriate for most mixed-source reporting.
Therefore, the correct techniques are Relationships and Cross-Database Joins.
* Tableau data modeling documentation recommending Relationships for multi-source modeling.
* Cross-database join support list including Excel + SQL Server.