# Data extension fields, data types and retention

*Marketing Cloud Engagement Foundations Study Guide · Data Management · Last updated November 3, 2026 · https://www.certifyforce.com/study-guide/marketing-cloud-engagement-foundations/data-management/data-extension-fields-data-types-and-retention*

The settings you choose when creating a data extension: properties and the external key, Create from Existing, sendable and testable options, field data types and lengths, primary keys, retention options and change control policies.

- Certification: Salesforce Marketing Cloud Engagement Foundations
- Exam section: Data Management
- Study guide: https://www.certifyforce.com/study-guide/marketing-cloud-engagement-foundations

**Official exam objective:**

> Configure settings when creating a new data extension, including settings for data fields.

## What the exam expects

- Set a new data extension's properties: creation method, name, external key, folder, Is Sendable and Is Testable.
- Choose the data type and length that fit each field's values.
- Decide which fields form the primary key and how a sendable data extension relates to subscribers.
- Pick the retention option that deletes the right data at the right time.
- Protect an important data extension with a change control policy.
- Key terms: **data extension** (a table of data you provide); **external key** (the unique identifier developers use in API calls); **primary key** (the field or fields whose values identify unique records); **send relationship** (the field that ties each row to a subscriber key or ID); **retention policy** (a setting that deletes records, or the whole table, after a period).

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Blank external key | A unique key is created for you | [Create a Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_data_extension.htm&type=5&language=en_US) |
| Create from Existing | Copies fields and configurations, not data | [Create from an Existing Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_de_from_de.htm&type=5&language=en_US) |
| Length setting | Text and Decimal only | [Create a Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_data_extension.htm&type=5&language=en_US) |
| Text maximum | 4,000 characters | [Data Extension Data Types](https://help.salesforce.com/s/articleView?id=mktg.mc_es_data_extension_data_types.htm&type=5&language=en_US) |
| Primary key value | Unique, at most 850 characters, fixed after creation | [Create a Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_data_extension.htm&type=5&language=en_US) |
| Subscriber key relationship | Text, Email Address or Phone field only | [Data Extension Properties](https://help.salesforce.com/s/articleView?id=mktg.mc_es_de_properties.htm&type=5&language=en_US) |
| All records retention | Deletes rows, keeps the data extension | [Create a Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_data_extension.htm&type=5&language=en_US) |
| Change control policy | Overrides user permissions | [Manage Policies](https://help.salesforce.com/s/articleView?id=mktg.mc_es_manage_de_policies.htm&type=5&language=en_US) |

## Check yourself

- Which dates can a Date field hold?
- When does a retention date move later on its own?
- Why would a 260-character address be rejected by an Email field?
- What are the largest precision and scale a Decimal field allows?

## Sources

- [Create a Data Extension in Email Studio](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_data_extension.htm&type=5&language=en_US)
- [Data Extension Data Types](https://help.salesforce.com/s/articleView?id=mktg.mc_es_data_extension_data_types.htm&type=5&language=en_US)
- [Create a Data Extension from an Existing Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_de_from_de.htm&type=5&language=en_US)
- [Data Extension Properties for Marketing Cloud Engagement](https://help.salesforce.com/s/articleView?id=mktg.mc_es_de_properties.htm&type=5&language=en_US)
- [Manage Policies for an Email Studio Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_manage_de_policies.htm&type=5&language=en_US)
- [Learn About Data Extensions (Trailhead)](https://trailhead.salesforce.com/content/learn/modules/marketing-cloud-contact-management/learn-about-data-extensions)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 9 linked practice questions, and unlimited timed mock exams are included with the Marketing Cloud Engagement Foundations pack (USD $19): https://www.certifyforce.com/practice-exams