SFDMU Help CenterCan autonumber fields be used as External IDs?
Answer.
Yes, you can use autonumber fields as an External Id, but only for the Insert operation.
- For operations that might include record updates, autonumber fields CANNOT be used as External Ids. This is because autonumber values are generated independently in each org, meaning they will never overlap between the Source and the Target orgs.
- If you use autonumber fields for insertions, it essentially does not matter. The plugin Can I omit the definition of External ID for an object?.