Cross-database joins in Tableau - Step-by-Step Guide

Introduction

Cross-database joins let you combine data from two different databases in one view. This helps when your data lives in separate places but you want to analyze it together without moving or copying it.

When your sales data is in one database and customer info is in another, and you want to see sales by customer details.

When you have product data in a cloud database and inventory data in a local database and want to analyze them together.

When you want to create a report that combines marketing campaign data from one system with website traffic data from another.

When you need to compare financial data stored in different databases without exporting and merging files manually.

When you want to build a dashboard that shows data from multiple sources side by side for better insights.

Steps

Step 1: Open Tableau Desktop and connect to your first data source

- Data Source page

The first data source appears in the canvas area

💡 Choose the database with the main data you want to analyze first

Step 2: Click 'Add' next to Connections to add a second data source

- Data Source page, Connections pane

A new connection window opens to select the second database

💡 You can connect to a different type of database here

Step 3: Select the second database and connect to it

- Connection window

The second data source appears alongside the first in the canvas

💡 Make sure you have access rights to both databases

Step 4: Drag a table from the first data source to the canvas

- Data Source page, canvas area

The table is added as the first table in the join

💡 This is usually your primary table

Step 5: Drag a table from the second data source onto the first table in the canvas

- Data Source page, canvas area

A join is created between the two tables across databases

💡 Tableau shows join options to choose the join type

Step 6: Click the join icon between the tables to set join type and keys

- Data Source page, join icon on canvas

Join configuration panel opens to select join type and matching fields

💡 Choose fields that exist in both tables and have matching data

Step 7: Verify the join results by previewing the data in the canvas

- Data Source page, data preview area

You see combined rows from both tables based on the join

💡 Check for unexpected duplicates or missing rows

Before vs After

Before

Data Source page shows only one database connection with its tables

After

Data Source page shows two database connections with tables joined across them, preview shows combined data

Settings Reference

Connection

📍 Data Source page, Connections pane

Select and connect to different databases for cross-database joins

Default: None

Join Type

📍 Data Source page, join icon between tables

Define how rows from each table match and combine

Default: Inner Join

Join Clauses

📍 Data Source page, join configuration panel

Specify which columns to use for matching rows between tables

Default: None

Common Mistakes

Trying to join tables without adding the second database connection first

Tableau cannot create a cross-database join without both data sources connected

Always add and connect to the second database before dragging its tables to join

Joining on fields that do not have matching data types or values

This causes no matching rows or incorrect join results

Check that join keys have compatible data types and matching values in both tables

Using a join type that excludes needed data

For example, using inner join when you need all rows from one table

Choose the join type carefully based on which rows you want to keep

Summary

Cross-database joins let you combine tables from different databases in one Tableau view.

You add multiple connections on the Data Source page and drag tables to join across them.

Choose join keys and join type carefully to get correct combined data.