HQL with Aggregate functions

Let us understand about Aggregate functions in HQL


Hibernate supports several aggregate functions similar to SQL aggregate functions.

Aggregate functions are used to get an aggregate value of any column like SUM(salary) from Employee table , AVG(salary) from Employee table

There are multiple such aggregate methods as below supported by Hibernate

AggregateFunctions_List

Let us perform some of these aggregate functions on Employee table by creating Hibernate Project.

Step 1

Create hibernate project

Please refer Hibernate setup in eclipse article on how to do it.

Project structure


HQLAggregate_Functions_ProjStructure

Step 2

Update pom.xml with Hibernate and Mysql dependencies

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
 
  <groupId>HQLAggregateFunctions</groupId>
  <artifactId>HQLAggregateFunctions</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
 
  <name>HQLAggregateFunctions</name>
  <url>http://maven.apache.org</url>
 
  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
 
  <dependencies>
 
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
 
     <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.2.6.Final</version>
        </dependency>
 
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>6.0.5</version>
        </dependency>
 
  </dependencies>
</project>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>HQLAggregateFunctions</groupId>
  <artifactId>HQLAggregateFunctions</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>HQLAggregateFunctions</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>

    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>

     <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-core</artifactId>
			<version>5.2.6.Final</version>
		</dependency>

		<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<version>6.0.5</version>
		</dependency>

  </dependencies>
</project>

Step 3

Create Employee class

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package com.kb.model;
 
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
 
@Entity
@Table(name="Employee")
public class Employee {
 
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    @Column(name = "Employee_Id")
    private int employeeId;
    
    @Column(name = "FirstName")
    private String firstName;
    
    @Column(name = "LastName")
    private String lastName;
    
    @Column(name = "Age")
    private int age;
    
    @Column(name = "Education")
    private String education;
    
    @Column(name = "Salary")
    private int salary;
    
    public int getEmployeeId() {
        return employeeId;
    }
    public void setEmployeeId(int employeeId) {
        this.employeeId = employeeId;
    }
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getEducation() {
        return education;
    }
    public void setEducation(String education) {
        this.education = education;
    }
    public int getSalary() {
        return salary;
    }
    public void setSalary(int salary) {
        this.salary = salary;
    }
}
package com.kb.model;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="Employee")
public class Employee {

	@Id
	@GeneratedValue(strategy = GenerationType.SEQUENCE)
	@Column(name = "Employee_Id")
	private int employeeId;
	
	@Column(name = "FirstName")
	private String firstName;
	
	@Column(name = "LastName")
	private String lastName;
	
	@Column(name = "Age")
	private int age;
	
	@Column(name = "Education")
	private String education;
	
	@Column(name = "Salary")
	private int salary;
	
	public int getEmployeeId() {
		return employeeId;
	}
	public void setEmployeeId(int employeeId) {
		this.employeeId = employeeId;
	}
	public String getFirstName() {
		return firstName;
	}
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}
	public String getLastName() {
		return lastName;
	}
	public void setLastName(String lastName) {
		this.lastName = lastName;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public String getEducation() {
		return education;
	}
	public void setEducation(String education) {
		this.education = education;
	}
	public int getSalary() {
		return salary;
	}
	public void setSalary(int salary) {
		this.salary = salary;
	}
}


We have specified Primary key as employeeId and generator class as “sequence” for automatic primary key generation.

Step 4

Create hibernate.cfg.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
       "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
       "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 
<hibernate-configuration>
 
   <session-factory>
 
       <!-- Database connection properties -->
       <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
       <property name="connection.url">jdbc:mysql://localhost/javainsimpleway</property>
       <property name="connection.username">root</property>
       <property name="connection.password">root</property>
 
       <!-- JDBC connection pool (using the built-in) -->
       <property name="connection.pool_size">100</property>
 
       <!-- SQL dialect -->
       <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
 
       <!-- Disable the second-level cache -->
       <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>
 
       <!-- Echo all executed SQL to stdout -->
       <property name="show_sql">true</property>
       
       <!-- Format the generated Sql -->
       <property name="format_sql">true</property>
 
       <!-- Dont Drop and re-create the database schema on startup,Just update it -->
       <property name="hbm2ddl.auto">update</property>
 
          <mapping class="com.kb.model.Employee" />
 
   </session-factory>
 
</hibernate-configuration>
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
       "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
       "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 
<hibernate-configuration>
 
   <session-factory>
 
       <!-- Database connection properties -->
       <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
       <property name="connection.url">jdbc:mysql://localhost/javainsimpleway</property>
       <property name="connection.username">root</property>
       <property name="connection.password">root</property>
 
       <!-- JDBC connection pool (using the built-in) -->
       <property name="connection.pool_size">100</property>
 
       <!-- SQL dialect -->
       <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
 
       <!-- Disable the second-level cache -->
       <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>
 
       <!-- Echo all executed SQL to stdout -->
       <property name="show_sql">true</property>
       
       <!-- Format the generated Sql -->
       <property name="format_sql">true</property>
 
       <!-- Dont Drop and re-create the database schema on startup,Just update it -->
       <property name="hbm2ddl.auto">update</property>
 
          <mapping class="com.kb.model.Employee" />
 
   </session-factory>
 
</hibernate-configuration>


We have defined all the database configuration in this file

hbm2ddl.auto property is defined in the config file which helps in automatic creation of tables in the database based on the mapping.

We have also provided the mapping class name using “mapping” tag.

Step 5

Create Hibernate util class

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package com.kb.util;
 
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
 
public class HibernateUtil {
    private static final SessionFactory sessionFactory = buildSessionFactory();
 
    private static SessionFactory buildSessionFactory() {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
            return new Configuration().configure().buildSessionFactory();
        } catch (Throwable ex) {
            // Make sure you log the exception to track it
            System.err.println("SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }
 
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
    
    public static void shutdown() {
        // Optional but can be used to Close caches and connection pools
        getSessionFactory().close();
    }
 
}
package com.kb.util;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
	private static final SessionFactory sessionFactory = buildSessionFactory();

    private static SessionFactory buildSessionFactory() {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
            return new Configuration().configure().buildSessionFactory();
        } catch (Throwable ex) {
            // Make sure you log the exception to track it
            System.err.println("SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
    
    public static void shutdown() {
    	// Optional but can be used to Close caches and connection pools
    	getSessionFactory().close();
    }

}

Step 6

Create PopulateData.java file to Populate Employee Table with initial data

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package com.kb.db;
 
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
 
import com.kb.model.Employee;
import com.kb.util.HibernateUtil;
 
public class PopulateData {
public static void main(String[] args) {
 
    // Get session factory using Hibernate Util class
    SessionFactory sf = HibernateUtil.getSessionFactory();
    // Get session from Sesson factory
    Session session = sf.openSession();
 
    // Begin transaction
    Transaction t = session.beginTransaction();
    
    //Create Employee  data
    Employee employee1 = new Employee();
    employee1.setFirstName("John");
    employee1.setLastName("KC");
    employee1.setAge(28);
    employee1.setEducation("PG");
    employee1.setSalary(25000);
    
    Employee employee2 = new Employee();
    employee2.setFirstName("Jacob");
    employee2.setLastName("JC");
    employee2.setAge(30);
    employee2.setEducation("PG");
    employee2.setSalary(30000);
    
    Employee employee3 = new Employee();
    employee3.setFirstName("Martin");
    employee3.setLastName("A");
    employee3.setAge(24);
    employee3.setEducation("UG");
    employee3.setSalary(20000);
    
    Employee employee4 = new Employee();
    employee4.setFirstName("Peter");
    employee4.setLastName("M");
    employee4.setAge(25);
    employee4.setEducation("UG");
    employee4.setSalary(22000);
    
    Employee employee5 = new Employee();
    employee5.setFirstName("Roshan");
    employee5.setLastName("B");
    employee5.setAge(29);
    employee5.setEducation("PG");
    employee5.setSalary(45000);
    
    
    session.save(employee1);
    session.save(employee2);
    session.save(employee3);
    session.save(employee4);
    session.save(employee5);
 
    // Commit the transaction and close the session
    t.commit();
    
    session.close();
    System.out.println("successfully persisted Employee details");
 
   }
 
}
package com.kb.db;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;

import com.kb.model.Employee;
import com.kb.util.HibernateUtil;

public class PopulateData {
public static void main(String[] args) {

	// Get session factory using Hibernate Util class
	SessionFactory sf = HibernateUtil.getSessionFactory();
	// Get session from Sesson factory
	Session session = sf.openSession();

	// Begin transaction
	Transaction t = session.beginTransaction();
	
	//Create Employee  data
	Employee employee1 = new Employee();
	employee1.setFirstName("John");
	employee1.setLastName("KC");
	employee1.setAge(28);
	employee1.setEducation("PG");
	employee1.setSalary(25000);
	
	Employee employee2 = new Employee();
	employee2.setFirstName("Jacob");
	employee2.setLastName("JC");
	employee2.setAge(30);
	employee2.setEducation("PG");
	employee2.setSalary(30000);
	
	Employee employee3 = new Employee();
	employee3.setFirstName("Martin");
	employee3.setLastName("A");
	employee3.setAge(24);
	employee3.setEducation("UG");
	employee3.setSalary(20000);
	
	Employee employee4 = new Employee();
	employee4.setFirstName("Peter");
	employee4.setLastName("M");
	employee4.setAge(25);
	employee4.setEducation("UG");
	employee4.setSalary(22000);
	
	Employee employee5 = new Employee();
	employee5.setFirstName("Roshan");
	employee5.setLastName("B");
	employee5.setAge(29);
	employee5.setEducation("PG");
	employee5.setSalary(45000);
	
	
	session.save(employee1);
	session.save(employee2);
	session.save(employee3);
	session.save(employee4);
	session.save(employee5);

	// Commit the transaction and close the session
	t.commit();
	
	session.close();
	System.out.println("successfully persisted Employee details");

   }

}


In this class, we are persisting 5 Employee records and we will perform aggregate operations on these records.

Step 7

Lets Create Main class to perform HQL Aggregate operations

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package com.kb.db;
 
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.Query;
 
import com.kb.util.HibernateUtil;
 
public class AggregateFunctions {
    public static void main(String[] args) {
        // Get session factory using Hibernate Util class
        SessionFactory sf = HibernateUtil.getSessionFactory();
        // Get session from Sesson factory
        Session session = sf.openSession();
 
        // Retrieve Max salary of Employee
        Query maxSalaryQuery = session.createQuery("SELECT MAX(salary) FROM Employee");
        Object maxSalary = maxSalaryQuery.getSingleResult();
        System.out.println("Maximum salary of Employee -> " + maxSalary);
 
        // Retrieve Min salary of Employee
        Query minSalaryQuery = session.createQuery("SELECT MIN(salary) FROM Employee");
        Object minSalary = minSalaryQuery.getSingleResult();
        System.out.println("Minimum salary of Employee -> " + minSalary);
 
        // Retrieve Average salary of Employee
        Query avgSalaryQuery = session.createQuery("SELECT AVG(salary) FROM Employee");
        Object avgSalary = avgSalaryQuery.getSingleResult();
        System.out.println("Average salary of Employees -> " + avgSalary);
 
        // Retrieve Number of Employees
        Query empCountQuery = session.createQuery("SELECT COUNT(*) FROM Employee");
        Object empCount = empCountQuery.getSingleResult();
        System.out.println("Total number of Employees -> " + empCount);
 
        // Retrieve Total Sum of salary of all Employees
        Query sumSalaryQuery = session.createQuery("SELECT SUM(salary) FROM Employee");
        Object sumSalary = sumSalaryQuery.getSingleResult();
        System.out.println("Total sum of salary of all Employees -> " + sumSalary);
 
        session.close();
    }
 
}
package com.kb.db;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.Query;

import com.kb.util.HibernateUtil;

public class AggregateFunctions {
	public static void main(String[] args) {
		// Get session factory using Hibernate Util class
		SessionFactory sf = HibernateUtil.getSessionFactory();
		// Get session from Sesson factory
		Session session = sf.openSession();

		// Retrieve Max salary of Employee
		Query maxSalaryQuery = session.createQuery("SELECT MAX(salary) FROM Employee");
		Object maxSalary = maxSalaryQuery.getSingleResult();
		System.out.println("Maximum salary of Employee -> " + maxSalary);

		// Retrieve Min salary of Employee
		Query minSalaryQuery = session.createQuery("SELECT MIN(salary) FROM Employee");
		Object minSalary = minSalaryQuery.getSingleResult();
		System.out.println("Minimum salary of Employee -> " + minSalary);

		// Retrieve Average salary of Employee
		Query avgSalaryQuery = session.createQuery("SELECT AVG(salary) FROM Employee");
		Object avgSalary = avgSalaryQuery.getSingleResult();
		System.out.println("Average salary of Employees -> " + avgSalary);

		// Retrieve Number of Employees
		Query empCountQuery = session.createQuery("SELECT COUNT(*) FROM Employee");
		Object empCount = empCountQuery.getSingleResult();
		System.out.println("Total number of Employees -> " + empCount);

		// Retrieve Total Sum of salary of all Employees
		Query sumSalaryQuery = session.createQuery("SELECT SUM(salary) FROM Employee");
		Object sumSalary = sumSalaryQuery.getSingleResult();
		System.out.println("Total sum of salary of all Employees -> " + sumSalary);

		session.close();
	}

}

Step 8

Run PopulateData.java class to create the initial data

Step 9

Check the output in MYSQL DB

E:\MySql_Install\bin
Mysql –u root –p
Enter password

Use javainsimpleway;

Select * from Employee;

populateAggregateDataOutput

We can see that Emploeyee table has 5 records.

Step 10

Run AggregateFunctions.java

Output



Download this project HQLAggregateFunctions.zip

About the Author

Karibasappa G C (KB)
Founder of javainsimpleway.com
I love Java and open source technologies and very much passionate about software development.
I like to share my knowledge with others especially on technology 🙂
I have given all the examples as simple as possible to understand for the beginners.
All the code posted on my blog is developed,compiled and tested in my development environment.
If you find any mistakes or bugs, Please drop an email to kb.knowledge.sharing@gmail.com

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