What is function of the HAVING clause within a SQL query?
The HAVING clause functions similar to a WHERE clause in that it is used to filter out rows of data that do not want in your query result. The important difference for HAVING occurs after the GROUP BY clause, meaning you can include aggregate functions as part of the condition to check
What are the differences between an interface and an abstract class?
An interface cannot contain implementation details, only method signatures that must be created by any class that implements the interface. A class can implement multiple interfaces. An abstract class can contain implementation details, but it can not be instantiated, it can only be inherited from. So a subclass would still need to inherit the abstract class in order to implement the base class. A class can only inherit from a single base class, abstract or otherwise