ImportDefinitionUpdateType

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

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.