Import updateRule parameter
Import definitions include an updateRule parameter, which specifies how Eloqua should handle updating records when you import a new value for an existing field. For example, if contact Sally Jones' email address in Eloqua is sally.jones9@example.com, and you import a new email address for Sally Jones, the updateRule determines whether Eloqua should retain the existing email address or replace it with the new one.
The following rule types are available:
always: Always update.ifNewIsNotNull: Update if the new value is not blank.ifExistingIsNull: Update if the existing value is blank.useFieldRule: Use the rule defined at the field level.
If you do not specify an updateRule, the rule type defaults to always.