JPQL Query gives exception when trying to add condition after order by

Question

I am trying to execute a MySql query in JPQL.
Here is my MySql Query

select * from test.employee order by DEG != 'm2',DEG;   

where test is schema name, employee is table name and DEG contains strings. I wrote this in JPQL and got exception.

EntityManagerFactory emFactory = Persistence.createEntityManagerFactory("DBConnectionPU");
EntityManager em = emFactory.createEntityManager();
Query q = em.createQuery("SELECT em FROM Employee em ORDER BY em.deg != 'm2', em.deg");
List<Employee> list = q.getResultList();   

Exception :

Exception Description: Syntax error parsing [SELECT em FROM Employee em ORDER BY em.deg != 'm2', em.deg]. 

[36, 50] The order by item is not a valid expression.
        at org.eclipse.persistence.internal.jpa.EntityManagerImpl.createQuery(EntityManagerImpl.java:1605)
        at dbconnection.DBConnection.main(DBConnection.java:39)
    Caused by: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.JPQLException
    Exception Description: Syntax error parsing [SELECT em FROM Employee em ORDER BY em.deg != 'm2', em.deg]. 
    [36, 50] The order by item is not a valid expression.
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.buildException(HermesParser.java:155)
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.validate(HermesParser.java:334)
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.populateQueryImp(HermesParser.java:278)
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.buildQuery(HermesParser.java:163)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.buildEJBQLDatabaseQuery(EJBQueryImpl.java:142)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.buildEJBQLDatabaseQuery(EJBQueryImpl.java:116)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.<init>(EJBQueryImpl.java:102)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.<init>(EJBQueryImpl.java:86)
        at org.eclipse.persistence.internal.jpa.EntityManagerImpl.createQuery(EntityManagerImpl.java:1603)
        ... 1 more   

I tried this using criteria query and it works fine. Whats wrong with it in straight JPQL query? Am I missing something ?

Answer 1

Try changing em.deg != 'm2' to case when :

SELECT em 
FROM Employee em 
ORDER BY CASE WHEN em.deg != 'm2' THEN 1 ELSE 0 END, em.deg