How can I use mysql null safe equality operator <=> in HQL?

问题

I wanted to get records of Patient(POJO class) who's contact number is not null. So, I referred this post.
In the answer two ways are specified

SELECT * 
FROM table 
WHERE YourColumn IS NOT NULL;   

SELECT *
FROM table 
WHERE NOT (YourColumn <=> NULL); 

From above I wrote below hql which runs successfully

from Patient p where p.contactNo is not null    

But, for 2nd type of hql

from Patient p where not (p.contactNo <=> null)

throws Exception

org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: >  

How can I use mysql null safe equality operator <=> in HQL?

回答1:

HQL is a different language than MySQL. MySQL operators are not necessarily available in HQL.

This being said, you can given Hibernate MySQL queries (provided your database is MySQL):

Query query = entityMangager.createNativeQuery("Some MySQL code");
List results = query.getResultList();

EntityManager is an interface from the Java Persistence API. Hibernate has a tutorial about using the JPA, but here are the main points:

In order to have an entity manager, you need META-INF/persistence.xml file in your classpath. Then, inside a Java EE container, you get an instance of this interface with the @PersistenceContext annotation:

@PersistenceContext(unitName = "persistenceUnit")
private EntityManager em;

Outside a Java EE container, you can get one with the Persistence class:

EntityManagerFactory factory = Persistence.createEntityManagerFactory("persistenceUnit");
EntityManager em = factory.createEntityManager();

In both case, "persistenceUnit" must be the name of a persistence unit defined in your persistence.xml file.

来源：https://stackoverflow.com/questions/19245502/how-can-i-use-mysql-null-safe-equality-operator-in-hql