Hibernate Joins

Hibernate Join

In this section, you will learn about types of joins in Hibernate.

What is Join in SQL?

A SQL join combines the matching records from the two database tables. The matching record is on the basis of some condition, which we will provide with the query. The simple SQL query is given below : (not for Hibernate)

SELECT Student.LastName, Student.FirstName, Enrollment.EnrollNo
FROM Student
INNER JOIN Enrollment
ON Student.EnrollNo=Enrollment.EnrollNo
ORDER BY Student.LastName

Join is of three types :

• Inner Join
  Inner Join returns the matching row/rows between the two tables. In Hibernate, the keyword is inner join. The complete query is given below : 
  

  select e.firstname,e.lastname,e.cellphone,a.city,a.state,a.country from Employee e
  inner join e.address as a

• Left Outer Join
  Left Outer Join returns all the records from the left table and only matching records from the right table. In Hibernate, the keyword is left join. The complete query is given below : 
  

  select e.firstname,e.lastname,e.cellphone,a.city,a.state,a.country from Employee e
  left join e.address as a

  
  
• Right Outer Join
  The Right Outer Join returns all the records from right table and only matching records from the left table. In Hibernate, the keyword is right join. The complete query is given below :
  

  select e.firstname,e.lastname,e.cellphone,a.city,a.state,a.country from Employee e
  right join e.address as a

• Full Join
  Full Join returns matching  records from both the table plus all the remaining records from both  the table. The full join is not usually useful.
  

For Complete tutorial on the above please go through the below links :

• Hibernate Inner Join
  
  
• Hibernate Left Outer Join
  
  
• Hibernate Right Outer Join