Salesforce.com Id attribute seems to have a 15 and 18 character value, whats the difference?

Question

When using the SOAP API to work with salesforce.com (SFDC) it seems that the primary key in the underlying database is Id. Well there seems to be two representations of this va

Answer 1

From the Web Services API Developer's Guide:

ID fields in the Salesforce.com user interface contain 15-character, base-62, case-sensitive strings. Each of the 15 characters can be a numeric digit (0-9), a lowercase letter (a-z), or an uppercase letter (A-Z). Two unique IDs may only be different by a change in case.

Because there are applications like Access which do not recognize that 50130000000014c is a different ID from 50130000000014C, an 18-digit, case-safe version of the ID is returned by all API calls. The 18 character IDs have been formed by adding a suffix to each ID in the Force.com API. 18-character IDs can be safely compared for uniqueness by case-insensitive applications, and can be used in all API calls when creating, editing, or deleting data.

If you need to convert the 18-character ID to a 15-character version, truncate the last three characters. Salesforce.com recommends that you use the 18-character ID.