Hibernate Query Language (HQL) Clauses

There are many HQL clauses available to interact with relational databases, and several of them are listed below:

FROM Clause
SELECT Clause
WHERE Clause
ORDER BY Clause
UPDATE Clause
DELETE Clause
INSERT Clause

For details and examples regarding each clause is mentioned below.

1. FROM Clause

To load a whole persistent object into memory, the FROM clause is used.

String hib = "FROM Student";

Query query = session.createQuery(hib);
List results = query.list();

2. SELECT Clause

The SELECT clause is used when only a few attributes of an object are required rather than the entire object.

String hib = "SELECT S.roll FROM Student S";

Query query = session.createQuery(hib);
List results = query.list();

3. WHERE Clause

Filtering records is done with the WHERE clause. It’s used to retrieve only the records that meet a set of criteria.

String hib = "FROM Student S WHERE S.id = 5";

Query query = session.createQuery(hib);
List results = query.list();

4. ORDER BY Clause

The ORDER BY clause is used to sort the results of an HQL query.

String hib = "FROM Student S WHERE S.id > 5 ORDER BY S.id DESC";

Query query = session.createQuery(hib);
List results = query.list();

NOTE:

1. Order By – DESC will sort in descending order

2. Order By – ASC will sort in ascending order

5. UPDATE Clause

The UPDATE clause is required to update the value of an attribute.

String hib = "UPDATE Student set name=:n WHERE roll=:i";

Query q=session.createQuery(hib);  
q.setParameter("n","John");  
q.setParameter("i",23);  

int status=q.executeUpdate();  
System.out.println(status);

6. DELETE Clause

It is required to delete a value of an attribute.

String hib = "DELETE FROM Student WHERE id=10";

Query query=session.createQuery(hib);  
query.executeUpdate();

7. INSERT Clause

It is required to Insert values into the relation.

String hib = "INSERT INTO Student(first_name, last_name)" +
                "SELECT first_name, last_name FROM backup_student";

Query query = session.createQuery(hib);
int result = query.executeUpdate();