What is design pattern (Adapt, Mediator and Proxy) for interface dependency

Given the scenario below where the DbConnection interface is intermediating two classes of implementations., which design pattern is it actually linked to, as it seems to be associated with 3 distinct design patterns in the case being Adapter, Proxy and Mediator. Can you help me ?

Scenario: I have a class called UserService to connect to the database and I created an interface called DbConnection where the UserService will connect. The DbConnection interface will currently only have one implementation called MySqlDbConnhection but I can change to the OracleDbConnection implementation in the future and the UserService will not be affected as it only knows the DbConnection interface.