Hibernate Query Language (HQL)

Hibernate Query Language (HQL) is an object-oriented query language, similar to SQL, but instead of operating on tables and columns, HQL works with persistent objects and their properties. HQL queries are translated by Hibernate into conventional SQL queries, which in turns perform action on database. Although you can use SQL statements directly with Hibernate using Native SQL, but I would recommend using HQL whenever possible to avoid database portability hassles, and to take advantage of Hibernates SQL generation and caching strategies. Keywords like SELECT, FROM, and WHERE, etc., are not case sensitive, but properties like table and column names are case sensitive in HQL.

Query Interface

It is an object-oriented representation of Hibernate Query. The object of Query can be obtained by calling the create Query () method Session interface. The query interface provides many methods. There is given commonly used methods:

Hibernate converts HQL queries into SQL queries, which are used to perform database actions. Although Native SQL may be used directly with Hibernate, it is encouraged to utilize HQL wherever feasible to prevent database portability issues.

HQL has many benefits. Some benefits are:

• HQL is database independent.
• polymorphic queries supported which are type safe.
• It is portable and easy to learn for Java programmers.

Hibernate Query Language (HQL) Clauses

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

1. FROM Clause
2. SELECT Clause
3. WHERE Clause
4. ORDER BY Clause
5. UPDATE Clause
6. DELETE Clause
7. INSERT Clause

Here are some benefits of using Hibernate Query Language (HQL): 

• Simplified data access: HQL abstracts the complexities of SQL queries and JDBC (Java Database Connectivity). This allows developers to interact with the database using Java objects instead of writing manual SQL statements. 
• Scalability: HQL is not specific to any database, making it easy to scale and migrate.
• Object-oriented: HQL is fully object-oriented and understands concepts like polymorphism, inheritance, and association. 
• Automatic primary key generation: Hibernate supports automatic key generation in tables with primary keys. This simplifies the code and eliminates the need to create fundamental values when inserting new records.
• Caching: Caching improves the performance of an application by storing frequently accessed data in memory.
• Exception handling: Hibernate wraps JDBC exceptions and throws unchecked exceptions. This, along with the built-in transaction management system, helps developers avoid writing multiple try-catch blocks to handle exceptions.

HQL is similar in appearance to SQL and supports many SQL-like features, such as sub-queries, JOINs, and group by.