What is JPQL in JPA?

JPQL stands for:

Java Persistence Query Language

JPQL is a query language used in JPA to fetch and manipulate data from the database using entity objects instead of table names.

In simple words:

“JPQL allows developers to write database queries using Java entity classes rather than SQL tables.”

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Why JPQL is Needed

In traditional SQL:

• Queries are written using table names
• Column names are used directly
• Database-specific syntax may vary

JPQL solves these problems by:

• Using entity names instead of table names
• Using object-oriented queries
• Providing database independence

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Simple Real-Time Example

Suppose:

• Student entity maps to students table

SQL query:

SELECT * FROM students;

Equivalent JPQL query:

SELECT s FROM Student s

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Main Difference Between SQL and JPQL

Feature	SQL	JPQL
Works On	Database tables	Entity classes
Uses	Table names	Entity names
Database Dependent	Yes	No
Object-Oriented	No	Yes

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Entity Example

@Entity
public class Student {

    @Id
    private Long id;

    private String name;

    private String email;
}

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Basic JPQL Query Example

SELECT s FROM Student s

Here:

• Student → Entity class
• s → Alias

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How JPQL Works Internally

1. Developer writes JPQL query
2. Hibernate converts JPQL to SQL
3. Database executes generated SQL
4. Results are mapped to entities

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Generated SQL Example

JPQL:

SELECT s FROM Student s

Hibernate generates:

SELECT *
FROM students

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Using JPQL in Spring Boot

JPQL is commonly used with:

• @Query annotation
• EntityManager

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@Query Example

@Query("SELECT s FROM Student s")
List<Student> getAllStudents();

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Find by Condition Example

@Query("""
SELECT s
FROM Student s
WHERE s.name = :name
""")
List<Student> findByName(String name);

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Generated SQL

SELECT *
FROM students
WHERE name = ?

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JPQL SELECT Query

Used to retrieve entity data.

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Example

SELECT s FROM Student s

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JPQL WHERE Clause

Used to filter data.

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Example

SELECT s
FROM Student s
WHERE s.email = :email

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JPQL ORDER BY Clause

Used to sort results.

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Example

SELECT s
FROM Student s
ORDER BY s.name ASC

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JPQL GROUP BY Clause

Used for grouping records.

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Example

SELECT s.department,
COUNT(s)
FROM Student s
GROUP BY s.department

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JPQL JOIN Query

JPQL supports entity relationships and joins.

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JOIN Example

SELECT o
FROM Order o
JOIN o.customer c
WHERE c.name = :name

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Generated SQL

SELECT o.*
FROM orders o
JOIN customers c
ON o.customer_id = c.id
WHERE c.name = ?

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JPQL FETCH JOIN

FETCH JOIN loads related entities immediately.

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FETCH JOIN Example

SELECT c
FROM Customer c
JOIN FETCH c.orders

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Why FETCH JOIN is Useful

It helps avoid:

• N+1 query problem
• Excessive lazy loading queries

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JPQL Named Parameters

JPQL supports named parameters using:

:parameterName

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Example

@Query("""
SELECT s
FROM Student s
WHERE s.name = :name
""")
Student findByName(
        @Param("name") String name
);

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JPQL Positional Parameters

JPQL also supports positional parameters.

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Example

@Query("""
SELECT s
FROM Student s
WHERE s.name = ?1
""")
Student findByName(String name);

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JPQL UPDATE Query

Used to update records.

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Example

@Modifying
@Query("""
UPDATE Student s
SET s.name = :name
WHERE s.id = :id
""")
void updateStudentName(
        Long id,
        String name
);

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JPQL DELETE Query

Used to delete records.

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Example

@Modifying
@Query("""
DELETE
FROM Student s
WHERE s.id = :id
""")
void deleteStudent(Long id);

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JPQL Aggregate Functions

JPQL supports functions such as:

• COUNT()
• SUM()
• AVG()
• MIN()
• MAX()

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COUNT Example

SELECT COUNT(s)
FROM Student s

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JPQL Pagination Example

Pageable pageable =
        PageRequest.of(0, 10);

studentRepository.findAll(pageable);

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Advantages of JPQL

• Database independent
• Object-oriented queries
• Supports entity relationships
• Readable and maintainable
• Integrated with Hibernate

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Disadvantages of JPQL

• Complex queries can become difficult
• Limited compared to native SQL
• Performance tuning may be harder

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Difference Between JPQL and Native SQL

Feature	JPQL	Native SQL
Uses	Entities	Tables
Database Independence	Yes	No
Complex SQL Features	Limited	Full support
Portability	High	Lower

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Real-Time Example in E-Commerce Application

E-commerce application contains:

• Customers
• Orders
• Products

JPQL helps:

• Fetch customer orders
• Generate reports
• Perform filtering and searching

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Best Practices for JPQL

• Use meaningful aliases
• Prefer named parameters
• Use FETCH JOIN carefully
• Optimize complex queries
• Use pagination for large datasets

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Common Interview Questions on JPQL

What is JPQL?

JPQL is an object-oriented query language used in JPA.

What is the difference between SQL and JPQL?

SQL uses table names, while JPQL uses entity classes.

What is FETCH JOIN?

FETCH JOIN loads related entities immediately.

Can JPQL perform UPDATE and DELETE operations?

Yes.

What are named parameters in JPQL?

Parameters prefixed with colon (:).

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Conclusion

JPQL is one of the most important features in JPA and Hibernate.

It allows developers to:

• Write object-oriented database queries
• Use entity relationships easily
• Build database-independent applications
• Reduce manual SQL coding

Understanding JPQL is essential for Spring Boot developers because enterprise applications heavily rely on efficient querying, filtering, reporting, and relationship handling.

Proper use of JPQL improves:

• Maintainability
• Scalability
• Performance optimization
• Developer productivity