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Joining Database Tables on Non-Foreign Key Fields Oct 13, 2023 by Robert Gravelle

In the world of relational databases, joining tables on foreign keys is a common and well-understood practice. However, there are situations where you need to join tables based on non-foreign key fields. This might seem unconventional, but it can be a powerful technique when used appropriately. In this article, we will explore the concept of joining database tables on non-foreign key fields, and we'll demonstrate how to do it using Navicat.

Why Join on Non-Foreign Key Fields?

In typical database design, tables are related using foreign keys, which establish clear relationships between data. However, there are scenarios where you might need to join tables based on fields that are not explicitly marked as foreign keys. Here are some reasons why you might consider this approach:

  • Data Enrichment: You may want to enrich your data by combining information from different tables based on some shared characteristics.
  • Legacy Databases: In legacy databases, foreign keys may not have been established, or the schema might not follow best practices.
  • Data Migration: During data migration or integration, you might need to join data from multiple sources.
  • Complex Queries: Some complex analytical or reporting queries may require joining tables on non-foreign key fields.

Using Navicat for Non-Foreign Key Joins

Navicat is a powerful database client that supports various database management systems like MySQL, PostgreSQL, SQL Server, and more. It provides a user-friendly interface for designing queries, making it an excellent choice for joining tables on non-foreign key fields.

Example: Combining Customer and Order Data

Let's consider a scenario where you have two tables: Customers and Orders. Normally, these tables would be related through a CustomerID foreign key field in the Orders table. However, in this example, we want to join them based on a shared Email field, which is not a foreign key.

To join the Customers and Orders tables on the Email field, you can use a SQL query like this:

SELECT Customers.*, Orders.*
FROM Customers
INNER JOIN Orders ON Customers.Email = Orders.CustomerEmail;

join_on_email (28K)

In this query:

  • Customers.* and Orders.* select all columns from both tables.
  • INNER JOIN combines rows with matching Email and CustomerEmail values.

Tips for Non-Foreign Key Joins

When joining tables on non-foreign key fields, consider the following tips:

  • Data Consistency: Ensure that the non-foreign key fields you're joining on have consistent data. In our example, the Email field should be consistently formatted and not contain missing or duplicate values.
  • Indexes: Consider creating indexes on the fields you're joining on. Indexes can significantly improve query performance.
  • Data Types: Ensure that the data types of the fields being joined match. For example, if you're joining on an email address, both fields should have the same data type, such as VARCHAR.
  • Testing: Always thoroughly test your queries to verify that the results are as expected, especially when joining tables on non-foreign key fields.


Joining database tables on non-foreign key fields is a flexible and powerful technique that can help you work with data in unconventional ways. Navicat provides an intuitive interface for crafting SQL queries that perform these joins, making it a valuable tool for database professionals and developers.

Remember that while joining on non-foreign key fields can be useful, it should be done thoughtfully and with attention to data quality and consistency. When used appropriately, this approach can unlock new insights and possibilities in your data analysis and reporting.

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