Blend Your Data - Tableau

Data Blending in Tableau Overview

Data blending in Tableau is a method to combine data from multiple sources into a single view, useful when relationships vary by sheet or when using published data sources.

Combining Data

Three Main Methods:

  1. Relationships: Default method; flexible but cannot link published data sources.

  2. Joins: Combine tables with additional columns before analysis; can result in data loss or duplication if detail levels differ and cannot link to published sources.

  3. Blends: Independently query data sources and present aggregated results, managing varying detail levels effectively.

Steps for Blending Data

  1. Connect to Multiple Data Sources: Add a second source via Data > New data source.

  2. Set Primary Data Source: Drag a field from the preferred primary source to the view.

  3. Add Secondary Data Source: Switch to the second source, link it to the primary, and drag a field into the view; a linking icon indicates connection.

  4. Using Linking Fields: Both data sources must have a linking field for blending, with options to fix any broken links.

  5. Identifying Sources: Primary source indicated by a blue check mark; secondary source by an orange check mark.

Understanding Primary and Secondary Data Sources

The primary data source restricts values from the secondary source, similar to a left join. Switching sources may be required for a full analysis.

Calculations Across Blended Data Sources

Calculations can be complex; fields from the secondary source are aggregated by default (SUM). All fields in a calculation must be aggregated to avoid errors, and dot notation references fields from other sources.

Defining Blend Relationships

Active linking fields must share values between data sources. Tableau links fields with matching names automatically; renaming or manual linking is possible if names differ.

Working with Multiple Links

More specific analysis is possible by defining relationships using multiple fields, but over-linking can drop data.

Differences Between Joins and Blends

Blending acts like a left join; the key difference is operational order: joins aggregate after combining, while blends aggregate first then combine.

Limitations of Data Blending

  • Handle non-additive aggregates carefully; COUNTD, MEDIAN, and RAWSQLAGG have issues.

  • Blended sources cannot be published as a single unit; each must be published separately.

  • All fields from secondary sources must be aggregated. Cube sources must be primary to blend correctly.

Conclusion

Data blending in Tableau efficiently visualizes data from multiple sources. Understanding how to manage data sources, define relationships, and navigate limitations is crucial for effective analysis.