BigData / Tableau Interview Questions
What is the difference between data blending and a join in Tableau?
Both let you combine two data sources, but they operate at different stages and with very different implications for how detailed your results can be.
| Join | Data Blending |
| Combines data at the row level, before aggregation. | Combines data at the visualization level, after aggregating the secondary source. |
| Both sources must typically be the same connection type. | Sources can be entirely different connection types (SQL + Excel, live + extract). |
| Full row-level detail available from all joined sources. | Secondary source detail is limited to the linking field's granularity. |
| Executed as part of the underlying query. | Executed as two separate queries, merged afterward. |
The rule of thumb: use a join whenever both sources can support it and you need full row-level flexibility; reach for blending only when a join isn't possible, keeping in mind its aggregation trade-off.
At what stage does a join combine two data sources, compared to blending?
Which technique allows connecting sources of entirely different connection types (e.g. SQL and Excel)?
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