It is not possible to merge contacts in your database.
The data in your contact records is complex and contains a variety of types of fields with different types of data. Because of this, it is not possible for the system to safely merge contacts programmatically.
If you wish to resolve duplicates, please refer to this article titled "Removing duplicate contacts".
More info
To keep your contacts organised we can recommend exploring the system's grouped contacts and organisation functionality. Read more:
1. Grouped Contacts
2. Grouping Contacts by Organisation and Relationship