For which data type we can enable external id?
I am learning for my 401 dev exam and reading the book For.com Developer Certification Handbook DEV401. This book is written a little weird and sometimes is even contradictory to itself. therefore I am not certain that all information is correct. At some point, it says:
A custom field can be marked as an external ID to identify the primary keys of the
legacy system (outside Salesforce). Text, number, e-mail, and auto-number fields can
be flagged as external IDs.
but this seems so weird. I mean, an auto-number is a number that is generated by Salesforce, why would you not want to keep track of one generated unique identifier (Salesforce ID) but then keep track of another unique identifier (auto-number). Does anybody know if this information is legitimate?
The answer to your question - for which data type we can enable external id is - Auto-number fields can be external IDs. I can think of at least one good reason. Salesforce.com might be the source of record without explicitly using salesforce.com ID values, which may be case insensitive depending on the other application, which can cause unwanted complications. Using an auto-number field avoids case-sensitive ID values that might otherwise confuse systems not designed to handle such ID values, like Excel (which is, by default, case sensitive).