Boost Performance with Oracle Foreign Key Index Support

Updated October 2025

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Introduction

Oracle foreign key index support means ensuring that every foreign key column has a corresponding index. While not mandatory, having such an index significantly improves performance. Fortunately, Hora makes it easy to detect missing indexes and create them with just a few clicks.

Here we’ve cloned the HR schema into HR1 to demonstrate how this works. There is a foreign key constraint requiring each job_id in the EMPLOYEES table to match a primary key in the JOBS table. It is supported by the index EMP_JOB_IX:

This index helps optimize queries such as the one below:

As shown in the Explain Plan, the index is used to efficiently filter out the SA_REP rows:

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What Happens Without the Index

Now let’s see what happens if we drop this index and re-execute the query:

After removing the index, the constraint shows nothing under “Index support” in Hora’s Constraints tab:

When we run the query again, the Explain Plan shows a significantly increased CPU cost, clearly demonstrating the impact of the missing index.

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Why Foreign Key Indexes Matter

Another important reason to keep indexes on foreign key columns is to prevent full table locks on the child table whenever a parent table’s primary key is updated or deleted.
Without an index, Oracle must lock the entire child table to maintain referential integrity, which can block concurrent transactions.
For a detailed conceptual explanation using the HR.DEPARTMENTS and HR.EMPLOYEES tables, refer to the Oracle Concepts Manual.

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How Hora Helps You Fix It

If you encounter a foreign key constraint that is not supported by an index, Hora makes it easy to correct the issue.
Simply open the Constraints tab, right-click the constraint, and choose “Create index on FK columns” from the context menu:

The dialog automatically fills in the relevant details for the selected constraint, saving you time and effort:

You can even replace the suggested index name, such as EMP_JOB_FK_IDX, with the original Oracle-supplied name (EMP_JOB_IX) before proceeding.
This seamless workflow ensures that your foreign keys are fully optimized without requiring manual SQL scripting.

We hope you agree that foreign key index support is a small step that delivers big performance benefits—and that Hora makes managing it effortless.

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