PQL stands for “Java Persistence Query Language.” It is a database query language used with the Java Persistence API (JPA) to interact with relational databases in a Java-based application. JPQL is similar to SQL (Structured Query Language) but is specifically designed for querying and manipulating objects in a JPA-managed data model. Here are some key points about JPQL:

1. Object-Oriented Query Language: JPQL is an object-oriented query language that operates on Java objects rather than database tables. It allows you to write queries based on the structure of your Java entities, including their relationships and attributes.

2. Entity-Based Queries: JPQL queries are primarily used to retrieve or manipulate entities (objects that represent database records) and their attributes.

3. Database Independence: JPQL provides database independence. You write queries in terms of your entity classes, and the JPA provider (e.g., Hibernate, EclipseLink) translates those queries into SQL statements specific to the database you’re using.

4. Syntax Similar to SQL: While JPQL is different from SQL in some aspects, its syntax is similar to SQL, making it relatively easy for developers familiar with SQL to learn.

5. Named Queries: JPQL queries can be defined as named queries in entity classes or XML configuration files. Named queries can be reused across multiple parts of the application.

6. Dynamic Queries: JPQL queries can also be constructed dynamically at runtime based on the specific criteria or conditions of the application.

7. Joins and Relationships: JPQL supports joins, navigation of relationships between entities, and specifying conditions using criteria like WHERE clauses.

8. Aggregate Functions: You can use JPQL to perform aggregate functions like SUM, AVG, COUNT, MAX, and MIN on attributes within your entities.