What is Data Blending?

Blending combines data from separate data sources into one view — a spreadsheet with a database table, for instance.

The mechanics matter, because blending is not a join. Tableau queries each source independently, aggregates each one to the level of detail of the view, then combines the aggregated results on a shared dimension called the linking field.

The first source used in the sheet becomes primary and gets a blue tick; others are secondary with an orange tick. The combination behaves like a left join from the primary, so rows in the secondary with no match simply do not appear.

Because each side is aggregated first, blending handles mismatched granularity well — daily sales against monthly targets, for example, where a row-level join would duplicate rows.