JPQL supports AVG, COUNT, MAX, MIN, and SUM aggregate functions in SELECT statements.

Examples

Entity

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private long salary;
    .............
}

Using Aggregate Functions

public class ExampleMain {
    private static EntityManagerFactory entityManagerFactory =
            Persistence.createEntityManagerFactory("example-unit");

    public static void main(String[] args) {
        try {
            persistEmployees();
            findEmployeeCount();
            findEmployeeAvgSalary();
            findEmployeeMaxSalary();
            findEmployeeMinSalary();
            findEmployeeSalariesSum();

        } finally {
            entityManagerFactory.close();
        }
    }

    public static void persistEmployees() {
        Employee employee1 = Employee.create("Diana", 3000);
        Employee employee2 = Employee.create("Rose", 4000);
        Employee employee3 = Employee.create("Denise", 1500);
        Employee employee4 = Employee.create("Mike", 2000);
        EntityManager em = entityManagerFactory.createEntityManager();
        em.getTransaction().begin();
        em.persist(employee1);
        em.persist(employee2);
        em.persist(employee3);
        em.persist(employee4);
        em.getTransaction().commit();
        em.close();
    }

    private static void findEmployeeCount() {
        System.out.println("-- Employee COUNT --");
        EntityManager em = entityManagerFactory.createEntityManager();
        Query query = em.createQuery(
                "SELECT COUNT(e) FROM Employee e");
        Long result = (Long) query.getSingleResult();
        System.out.println(result);
        em.close();
    }

    private static void findEmployeeAvgSalary() {
        System.out.println("-- Employee AVG Salary --");
        EntityManager em = entityManagerFactory.createEntityManager();
        Query query = em.createQuery(
                "SELECT AVG(e.salary) FROM Employee e");
        Double result = (Double) query.getSingleResult();
        System.out.println(result);
        em.close();
    }

    private static void findEmployeeMaxSalary() {
        System.out.println("-- Employee MAX Salary --");
        EntityManager em = entityManagerFactory.createEntityManager();
        Query query = em.createQuery(
                "SELECT MAX(e.salary) FROM Employee e");
        Long result = (Long) query.getSingleResult();//salary of type long
        System.out.println(result);
        em.close();
    }

    private static void findEmployeeMinSalary() {
        System.out.println("-- Employee MIN Salary --");
        EntityManager em = entityManagerFactory.createEntityManager();
        Query query = em.createQuery(
                "SELECT MIN(e.salary) FROM Employee e");
        Long result = (Long) query.getSingleResult();//salary of type long
        System.out.println(result);
        em.close();
    }

    private static void findEmployeeSalariesSum() {
        System.out.println("-- Employee SUM Salary --");
        EntityManager em = entityManagerFactory.createEntityManager();
        Query query = em.createQuery(
                "SELECT SUM(e.salary) FROM Employee e");
        Long result = (Long) query.getSingleResult();
        System.out.println(result);
        em.close();
    }
}

-- Employee COUNT --
4
-- Employee AVG Salary --
2625.0
-- Employee MAX Salary --
4000
-- Employee MIN Salary --
1500
-- Employee SUM Salary --
10500

Example Project

Dependencies and Technologies Used:

• h2 1.4.197: H2 Database Engine.
• hibernate-core 5.2.13.Final: The core O/RM functionality as provided by Hibernate.
  Implements javax.persistence:javax.persistence-api version 2.1
• JDK 1.8
• Maven 3.3.9