Create an external ID field
Add an external ID field to an object's definition in Salesforce.com, and then include the external ID filed when you map your script.
- In a browser, log in to Salesforce.com.
- Near the top of the screen, click your user name, and then click Setup.
- Under Build, click Customize, and then select the object you want to update—for example, Account.
- Click the Add a custom field to accounts link.
- In the Account Custom Fields & Relationships section, click New.
- In the Data Type list, select a data type for the field—for example, Text—and then click Next.
- Enter the details for the field—for example, Field Label, Length, Field Name, Description.
If you want values to be case-sensitive, and check Do not allow duplicate values box, and then click Treat "ABC" and "abc" as different values (case sensitive).
- Check the External ID box, and click Next.
- Set the field-level security, which determines who can access this field, click Next, and then click Save.
The external ID is created and appears in the list under Account Custom Fields and Relationships.