What is the difference between HQL and SQL in Hibernate framework?

HQL and SQL are compared in the Hibernate framework: HQL (1. Object-oriented syntax, 2. Database-independent queries, 3. Type safety), while SQL directly operates the database (1. Database-independent standards, 2. Can perform complex queries and data operations).

HQL vs. SQL: Comparison in the Hibernate Framework

Introduction

Hibernate is a popular Java object-relational mapping (ORM) framework that allows developers to interact with databases using HQL (Hibernate Query Language). At the same time, developers can also use SQL to directly operate the database. This article will explore the differences between HQL and SQL in Hibernate and illustrate it through practical cases.

HQL

HQL is a SQL-like language for retrieving and manipulating persistent entities. It allows developers to use object-oriented syntax to query the database, thus simplifying the query process. HQL is based on the Java Persistence Query Language (JPQL) specification, which provides a database-independent query method.

SQL

SQL (Structured Query Language) is a standard language for interacting with relational databases. It provides a wide range of query and data manipulation capabilities, operating directly at the database level. Using SQL, developers can perform complex queries, create and modify tables, and make data updates.

Difference

The following are the main differences between HQL and SQL in Hibernate:

• Abstraction level: HQL It is unique to Hibernate and is based on Java syntax, while SQL is a database-independent standard.
• Type Safety: HQL is type safe because it uses Java data types, whereas SQL relies on database-specific data types.
• Object-oriented: HQL allows entities to be queried using object-oriented syntax, while SQL operates on tables and columns.
• Database portability: HQL offers database non-portability, which means that the same HQL query can be executed against different databases, while the SQL must be adapted to the specific database.

Practical Case

Consider the following query example:

// HQL 查询
String hqlQuery = "FROM Person WHERE name LIKE '%John%'";
Query hqlQuery = session.createQuery(hqlQuery);

// SQL 查询
String sqlQuery = "SELECT * FROM Person WHERE name LIKE '%John%'";
SQLQuery sqlQuery = session.createSQLQuery(sqlQuery);

// 执行查询
List<Person> hqlResults = hqlQuery.list();
List<Object[]> sqlResults = sqlQuery.list();

// 处理结果
// ...

In the above example:

• HQL The query uses object-oriented syntax (FROM Person) and uses Java data types (String).
• SQL queries operate directly on tables and columns (SELECT * FROM Person) and use SQL data types (LIKE '%John%').

Choose HQL or SQL

The choice between HQL or SQL in Hibernate depends on the specific use case. In general, it is recommended to use HQL for the convenience of object-oriented queries, type safety, and database non-portability. However, in some cases, you may need to use SQL to access more advanced functionality, such as native SQL functions or low-level table operations.

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