Detailed explanation of pure SQL statement method based on JPQL

JPQL stands for Java Persistence Query Language.

Based on the EJB Query Language (EJB QL) first introduced in EJB 2.0, the Java Persistence Query Language (JPQL) is a portable query language designed to bind SQL syntax and simple query semantics together in the form of object-oriented expression language expressions. Queries written in this language are portable and can be compiled into SQL on all major database servers.

Its features are similar to native SQL statements and are fully object-oriented, accessed through class names and attributes rather than table names and table attributes.

To use JPQL, you need to modify the SQL statement to be similar to HQL statement. SQL queries the database, while JPQL queries objects and attributes, and the syntax is somewhat different. For some queries that cannot be written in JPQL, it is more convenient to write them in native SQL.

Here is an example, note the difference in syntax:

JPQL Query

@PersistenceContext
protected EntityManager em;

public List<Video> findVideoList1() {
  String hql = "from Video order by id desc";
  Query query = em.createQuery(hql);
  List<Video> result = query.getResultList();
  em.clear();
  return result;
}

SQL Query

Query the data for the last 7 days

public List<Video> findVideoList2() {
  List<Video> result = (List<Video>) em.createNativeQuery
    ("select * from db_video where date_sub(curdate(), interval 6 day) <= date(date) order by date desc", Video.class)
    .getResultList();
  return result;
}

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