External ID fields for matching integrated records
Key Takeaway
Mark the field an integration matches on as both External ID and Unique, so upserts update the right record instead of creating duplicates.
An External ID is a custom field that stores a record's identifier from a system outside Salesforce, such as an ERP or billing system. Imports and integrations use it to find the matching Salesforce record without knowing the record's Salesforce ID. The integration can then update the right record instead of creating a duplicate.
What an External ID field is
An External ID field holds the unique identifier that a record has in an outside system.
Your org links Salesforce with Oracle Financials. You create an External ID field on Account to capture and display each account's Oracle ID, such as ORA-10442. An integration can then find the Salesforce account by its Oracle ID.
Only custom text, number, or email fields can be marked as External ID. Marking a field as External ID also indexes it, so selective filters on the field run quickly and the field is searchable in Salesforce.