External id may be used to reference an id from another external system.

Advantages:-

We can search id in salesforce.

we can use upsert API call via data loader.

upsert means =Update and Insert

How will the system identify whether the record is existing or not; either through an id and an external id.

Scenario:-

In day 1-When importing the data; first setup the batch size and after select the upsert method and importing the data in always csv format.


if data is updating it means that id has already exists but when data is inserting it means that id is not existing in salesforce .


These scenario are called External Field.