# Introduction to the Unique Check

Source: https://userguide.qualytics.io/data-quality-checks/unique/introduction/

*Requires the Data Quality (DQ) module.*

The Unique check asserts that no value repeats in a field, or that no combination of values repeats across a set of fields. Use it to enforce primary-key semantics, catch double-loaded rows, and guard composite keys on junction and line-item tables.

This section is the complete guide to the check. The Deep Dive covers the definition, properties, and full evaluation semantics, explains how anomalies are reported, walks through production examples, and collects best practices; the How-tos are step-by-step tutorials for creating, editing, and deleting a check; the API page documents the payload for programmatic use; and the FAQ answers the most frequent questions.

## Next Steps

- **How It Works**

  The complete reference: definition, field scope, single-field and composite semantics, NULL handling, filter behavior, and coverage.

  [How It Works](https://userguide.qualytics.io/data-quality-checks/unique/deep-dive/how-it-works/)
- **Anomaly Reporting**

  The anomaly message the check produces, what the counts mean, and how duplicate groups appear in Source Records.

  [Anomaly Reporting](https://userguide.qualytics.io/data-quality-checks/unique/deep-dive/anomaly-reporting/)
- **Examples**

  Production scenarios with sample data, duplicate groups, and the resulting anomaly messages.

  [Examples](https://userguide.qualytics.io/data-quality-checks/unique/deep-dive/examples/)
- **Best Practices**

  Guidelines for NULL handling, composite keys, scoping, and pairing rules.

  [Best Practices](https://userguide.qualytics.io/data-quality-checks/unique/deep-dive/best-practices/)
- **Permissions**

  The team permission each action needs: view, create, edit, archive, restore, and delete.

  [Permissions](https://userguide.qualytics.io/data-quality-checks/unique/deep-dive/permissions/)
- **Create a Check**

  Step-by-step tutorial for creating a Unique check on a single field or a composite key.

  [Create a Check](https://userguide.qualytics.io/data-quality-checks/unique/how-tos/create-a-check/)
- **Edit a Check**

  Step-by-step tutorial for changing the key, filter, coverage, or organizational properties.

  [Edit a Check](https://userguide.qualytics.io/data-quality-checks/unique/how-tos/edit-a-check/)
- **Delete a Check**

  Step-by-step tutorial for archiving a check and deleting it permanently.

  [Delete a Check](https://userguide.qualytics.io/data-quality-checks/unique/how-tos/delete-a-check/)
- **Troubleshooting**

  Common problems with NULLs, composite keys, counts, and anomaly reporting, and how to resolve them.

  [Troubleshooting](https://userguide.qualytics.io/data-quality-checks/unique/troubleshooting/)
- **API**

  Payload shape and field notes for creating a Unique check programmatically.

  [API](https://userguide.qualytics.io/data-quality-checks/unique/api/)
- **FAQ**

  Short answers to questions about NULLs, composite keys, coverage, and anomaly reporting.

  [FAQ](https://userguide.qualytics.io/data-quality-checks/unique/faq/)

*Last updated: October 19, 2026.*