---
schema_version: "1"
id: e33bfadce7a7510915edbbdc013f7b414f075cfe39ea21ccf052136142d5dfdd
title: Import or Copy a Large Dataset Using a Data Extension as the Source
collection: admin
version: current
locale: en-us
portal_url: https://docs.salesforce.com/admin/current/en-us/mktg/264-0-0/mc_as_copy_large_datasets_using_data_extension.md
canonical_url: https://help.salesforce.com/s/articleView?id=mktg.mc_as_copy_large_datasets_using_data_extension.htm&release=264.0.0&type=5
source_site: help.salesforce.com
content_type: documentation
content_hash: b0201a65485a80cbd589aaa70559af72fd442719cf1a034d3c26af8a5789e5e0
description: Use the Data Copy or Import activity to copy data between data extensions and eliminate the need for complex SQL queries. You can use a data extension as the source to update another data extension but not a subscriber list. To update a subscriber list, use an external file.
products:
  - Marketing
  - Marketing Cloud Engagement
release: "264"
---
# Import or Copy a Large Dataset Using a Data Extension as the Source

Use the Data Copy or Import activity to copy data between data extensions and eliminate the need for complex SQL queries. You can use a data extension as the source to update another data extension but not a subscriber list. To update a subscriber list, use an external file.

![Note](https://sf-zdocs-cdn-prod.zoominsoftware.com/tdta-mktg-mc_journeys_and_automations-264-0-0-production-enus/e08cdd71-c1c1-4ae5-a5e9-8a6dad583ad4/images/icon_note.png)

Note When you import a DateTime value from a data extension, millisecond information isn’t included in the import.

1. From the Activities page, click **Create Activity**.
2. Select **Data Copy or Import**.
3. Click **Create New Copy or Import Definition**, and provide the details.
    
     
    | Property | Detail |
    | --- | --- |
    | Name | Enter a unique name. |
    | Description | Identify the activity so that others using the account know what it is. |
    | External Key | Enter a value that uniquely identifies the activity when using the API. |
    | Notification Settings | To receive notifications for this activity, enter an email address. |
4. For the data source, select **Data Extension**, and select the data extension that you want to use.
5. Select the source data extension to copy data from, and click **Next**.
6. Select the target data extension to copy the data to, and click **Next**.
7. Select the data action and specify how to write data to the destination. Unless you choose to overwrite the existing data, the target data extension must have at least one primary key column.
    
     
    | Data Action | Details |
    | --- | --- |
    | Add Only | New data is added to the destination, and existing data isn’t updated. |
    | Update Only | Existing data is updated in the destination, and new data is ignored. |
    | Add and Update | New data is added to the destination, and existing data is updated. |
    | Overwrite (Data Extensions Only) | All data in the destination is replaced with data from the import file. You can’t recover overwritten data. |
8. Select how to map the data.
    
     
    | Mapping Option | Details |
    | --- | --- |
    | Map by Header Row | Each column header in the source data extension must match the column name in the target data extension. |
    | Map Manually | Each column header in the target data extension is mapped according to the source data extension. |
9. Click **Next**.
10. Run the activity.
11. On the Contact Builder Data Extension tab, verify the updates.

#### See Also

- [Import or Copy a Large Dataset Using an External File as the Source](https://help.salesforce.com/s/articleView?id=mktg.mc_as_update_a_list_or_data_extension_using_an_external_file.htm&release=264.0.0&type=5 "Use an external file with the Automation Studio Data Copy or Import (formerly Import File) activity to update a list or data extension.")