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JPQL

Basic Java
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JPQL addresses Entities, not tables directly

JPQL resembles SQL, but the query is written in terms of the persistence model. An Entity name is used instead of a table name, and its persistent fields or properties are used instead of columns. 

List<User> users = entityManager.createQuery(
        "select u from User u where u.active = :active",
        User.class)
    .setParameter("active", true)
    .getResultList();

Here User is an Entity, u.active is its attribute, and the result is immediately typed as List<User>. The provider translates JPQL into a query for the specific database.

Parameters are passed separately from query text

As with PreparedStatement, values should not be concatenated into the query string. The named parameter :active makes the query clearer and separates its structure from its data.

Relationships can be used directly in expressions

List<Order> orders = entityManager.createQuery(
        "select o from Order o where o.user.id = :userId",
        Order.class)
    .setParameter("userId", 42L)
    .getResultList();

JPQL can navigate mapped Entity relationships. But convenient object-oriented syntax does not remove the cost of the resulting SQL, so complex queries still need to be evaluated from the database point of view.

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