What is the difference between JPQL and HQL?

JPQL (Java Persistence Query Language) is a standardized query language for Java Persistence API (JPA). HQL (Hibernate Query Language) is a query language specific to the Hibernate framework.

Main differences:

• Standardization: JPQL is part of the JPA standard, HQL is specific to Hibernate.
• Support for features: HQL can include Hibernate-specific functions and capabilities that may be absent in JPQL (e.g., criteria.setResultTransformer).
• Performance: In most cases, performance is comparable since both languages are translated into SQL. However, some optimizations may be specific to the implementation (Hibernate in the case of HQL).
• Portability: JPQL is more portable across different JPA implementations (Hibernate, EclipseLink, OpenJPA), whereas HQL is tied to Hibernate.

Example of a simple query in both languages:

// JPQL
SELECT p FROM Product p WHERE p.price > 100

// HQL
SELECT p FROM Product p WHERE p.price > 100

Although the syntax of simple queries often matches, in more complex scenarios HQL may offer additional capabilities not provided by the JPQL standard. Using JPQL is recommended to ensure maximum portability of the application across different JPA providers.