Table of Contents

Relationship Columns Must Have Same Data Type

  • 2026-01-09
  • Morten Lønskov

Overview

This best practice rule identifies relationships where the connected columns have mismatched data types. Both columns in a relationship must share the same data type to ensure proper filtering, prevent errors, and maintain optimal query performance.

  • Category: Error Prevention

  • Severity: High (3)

Applies To

  • Relationships

Why This Matters

Relationships with mismatched data types cause serious problems:

  • Model validation errors: The model may fail to save or deploy
  • Relationship creation failures: Power BI and Analysis Services may reject the relationship
  • Implicit conversions: Expensive data type conversions on every query
  • Incorrect results: Type coercion leads to unexpected filtering behavior
  • Performance degradation: Converting data types during queries slows execution
  • Memory overhead: Additional memory required for conversion buffers

When This Rule Triggers

The rule triggers when:

FromColumn.DataType != ToColumn.DataType

This detects relationships connecting columns with different data types.

How to Fix

Manual Fix

  1. Identify which column should change data type
  2. Change the data type in Power Query, in the underlying data source or in the model
  3. Delete the existing relationship
  4. Create a new relationship between the corrected columns
  5. Verify filtering works correctly

Common Causes

Cause 1: Inconsistent Data Type Choices

Different data types chosen for the same logical key during import or table creation.

Cause 2: Source System Differences

Foreign keys imported from different source systems with different type conventions.

Cause 3: DateTime vs Date Mismatch

Fact tables using DateTime columns while date dimensions use Date type.

Example

Before Fix

Relationship: Sales[CustomerID] (Int64) → Customers[CustomerID] (String)

Error: Relationship fails validation or creates performance issues with implicit conversion

After Fix

Relationship: Sales[CustomerID] (Int64) → Customers[CustomerID] (Int64)

Result: Relationship works efficiently with no type conversion overhead

Compatibility Level

This rule applies to models with compatibility level 1200 and higher.