Tableau SQL Union - Step-by-Step Guide

Combining multiple datasets in Tableau is a common need for business analysts and data teams, especially when unified views and integrated dashboards are critical for decision-making. While Tableau offers data blending, using SQL UNION unlocks powerful integrations right at the data source level—ideal for scalable BI analytics and advanced reporting scenarios. However, writing reliable SQL UNION queries often challenges even experienced users. AI2sql makes this process seamless, generating BI-ready SQL UNION queries instantly—no advanced SQL skills required—while ensuring compatibility with Tableau and enterprise data sources.

Tableau SQL Union Overview and Benefits

• What is SQL UNION? – Combines results from two or more SELECT queries into a single unified dataset.

• When to use in Tableau? – Merge data from similar tables (e.g., sales by region, quarterly reports) for consistent visualization.

• Key BI Benefits:

  • Integrate disparate data sources for complete analysis

  • Power multi-source dashboards with unified metrics

  • Streamline ETL by handling data stitching in your SQL layer

BI Use Case Example

• Combine Q1, Q2, Q3 sales tables to show annual performance on a single Tableau dashboard using a SQL UNION.

Setting Up SQL Connections

1. Connect Tableau to your SQL database (MySQL, PostgreSQL, SQL Server, etc.).

2. Select 'New Data Source' and choose your database type.

3. Authenticate using your credentials (username/password, SSO, or OAuth as appropriate).

4. Test the connection to ensure access to all relevant tables.

For enterprise BI deployments, ensure you have the appropriate database permissions and access levels defined by IT or database administrators.

Writing Custom SQL Queries

1. On the Tableau Data Source page, click 'New Custom SQL'.

2. Paste your SQL UNION query (see examples below).

3. Click 'OK' to preview the unified data set before using it in worksheets and dashboards.

SQL UNION Examples in BI Scenarios

• Example 1: Simple UNION of Two Tables
  
  

  Use case: Visualize total revenues for H1 across all regions in one dashboard chart.

• Example 2: UNION ALL for Duplicates
  
  

  Use case: Track all purchase events including duplicates for activity heat maps.

• Example 3: UNION with Different Column Names (use aliases)
  
  

  Use case: Aggregate payroll expenses across regions with differing schema names.

• Example 4: UNION in Subquery for KPI Calculation
  
  

  Use case: Dashboard splits KPIs per department, blending online and offline sales.

• Example 5: UNION of Quarterly Datasets for Yearly Dashboard
  
  

  Use case: Single trend line showing all quarters in one Tableau visualization.

Advanced SQL Techniques and Best Practices

• Schema Consistency: Ensure each SELECT in your UNION outputs the same columns/types.

• Performance: Use UNION ALL for faster performance when duplicate removal is unnecessary.

• Parameterization: Use Tableau parameters to swap tables or time periods dynamically in your UNION queries.

• Security & Governance: Limit access to sensitive columns in custom SQL for enterprise compliance.

Troubleshooting Tips

• Column Mismatch: Check SELECT field order and types in each UNION query.

• Permission Errors: Verify Tableau user permissions in your source database.

• Caching: Refresh Tableau extracts after modifying UNION queries to view changes.

AI2sql: Generate BI-Ready Queries Instantly

• Describe your data combination (e.g., 'Combine sales from US and EU tables for last year')

• AI2sql instantly produces production-grade, Tableau-compatible SQL UNION queries

• No manual SQL knowledge required—even for complex multi-table BI needs

• Works across all enterprise and SMB SQL databases integrated in Tableau

Generate Tableau SQL Union queries instantly with AI2sql - no SQL expertise required for advanced BI analytics.

Screenshot Example

Imagine a Tableau dashboard where a single chart merges regional sales—including filters by product line and year—powering cross-team insights, all built on a custom SQL UNION query. (For step-by-step visual walkthroughs and more advanced tutorials, see Advanced Tableau SQL Union Techniques.)

Next Steps: Boost Tableau Analytics with AI2sql

• Combine disparate data tables with ease

• Speed up dashboard development and reduce errors

• Empower business users to create complex analytics without SQL learning curve

• Integrate seamlessly with your BI workflows and compliance processes

Used by data analysts worldwide, the AI2sql platform works with Tableau and all enterprise SQL sources—delivering BI-ready queries, reliably and fast.

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