# ImportDefinitionUpdateType

The merge and overwrite behaviors available when an import definition runs against a list or data extension.

## Values

| Name                | Description                                                                                                                                                                                               |
| ------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `AddAndDoNotUpdate` | Indicates that the import adds new subscribers but ignores existing subscribers. This property applies to both subscriber lists and data extensions. It corresponds to the **Add Only** option.           |
| `AddAndUpdate`      | Indicates that the import adds new subscribers and updates existing subscribers. This property applies to both subscriber lists and data extensions. It corresponds to the **Add and Update** option.     |
| `ColumnBased`       | Indicates that information in the import is updated based on column values.                                                                                                                               |
| `Merge`             | Not used.                                                                                                                                                                                                 |
| `Overwrite`         | Indicates that the import overwrites all existing data. This property applies to data extensions, and it can be used only if the primary key is unavailable.                                              |
| `UpdateButDoNotAdd` | Indicates that the import updates existing subscribers but doesn’t add new subscribers. This property applies to both subscriber lists and data extensions. It corresponds to the **Update Only** option. |

## Related Items

- [ImportDefinition](/docs/marketing/marketing-cloud/guide/importdefinition.md)