Duplicate contacts are several contacts corresponding to one person or company. Such duplicate contacts are sometimes created when they are added by different methods to the database; e.g., during signup on the website, subscription to newsletters, manual adding of a contact via Contacts app, importing contacts from various sources, etc. Having duplicate contacts is not good, because they do not allow you to view all related information about a person or a company in one common profile.
For example, shoppers often do not want to create a permanent account in online stores. Instead, they prefer to place orders without registration by simply entering the same contact details each time. This is convenient for a customer, but this convenience results in additional issues for the online store owner. Tracking a customer's order history and detecting regular customers becomes more complicated. Other marketing related issues arise as well; e.g., you cannot automatically offer a discount for the second order, bonuses are not accumulated in the affiliate program, etc.
The built-in tool for finding and merging duplicate contacts will help you to know how many regular customers you have. It is most efficient to compare contacts by their main identification fields such as email, full name, phone number. There are also other personal fields, which, however, are not suitable for exact contact identification: e.g., address or date of birth. This is why you can find duplicate contacts in Contacts app using only the following fields:
Full person name
If there are duplicate contacts in your database, then the duplicates merging tool will display them as several groups, each group corresponding to one person or company for which duplicate contacts have been found by the specified field.
Duplicate contacts within all found groups can be merged automatically. In this mode the most recently added contact is considered the primary one while others are treated as secondary contacts.
You can also merge duplicate contacts manually using the "Merge this group" link. On the group-viewing page you can select the desired primary contact and merge it with other, secondary, contacts in this group.
What happens when contacts are merged?
Contacts can have single fields and multi-fields. A single field can store only one value; e.g., name or gender. A multi-field can store several values; e.g., email address, phone number, postal address, because each contact can have more than one of them.
When contacts are merged, single fields of the primary contacts have the highest priority. Secondary contacts will lose their single-field values after merging. However, if the primary contact does not contain any value in a single field (e.g., gender is not specified), a corresponding value will be copied from one of secondary contacts to the primary contact.
With multi-fields, merging is much simpler. During merging, all their values are added to the primary contact. For example, if each of the merged duplicate contacts has a different email address, then the merged contact will store all their email addresses in one multi-field.
If the merged contacts have connections with other apps; e.g., Helpdesk, Mailer, Hub, then those references will be updated to point to the resulting primary contact, which will remain after merging.