About query

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JPA Doc
111

Criteria Query Expressions

The following interfaces are in use in representing general expressions in criteria queries: See the Query Expressions section for more details and examples.
JPA Doc
111

JPA Annotations for SQL Queries

The following JPA annotations are designated for SQL queries on relational databases: ObjectDB supports only the preferred JPA query language, JPQL, and silently ignores all the above annotations.
Manual
82

FROM clause (JPQL / Criteria API)

The FROM clause declares query identification variables that represent iteration over objects in the database. A query identification variable is similar to a variable of a Java enhanced for loop in a program, since both are used for iteration over objects. Range Variables Range variables are query
Manual
82

SELECT clause (JPQL / Criteria API)

, the following query returns Country objects that become managed by the EntityManager em: TypedQuery query = em.createQuery("SELECT c FROM Country c", Country.class); List results = query.getResultList(); Because the results are managed entity objects they have all the support
Manual
69

GROUP BY and HAVING clauses

The GROUP BY clause enables grouping of query results. A JPQL query with a GROUP BY clause returns ... clause in the query execution order is after the FROM and WHERE clauses, but before the SELECT clause. When a GROUP BY clause exists in a JPQL query, database objects (or tuples of database objects
Manual
68

CRUD Database Operations with JPA

persisting objects in the database in more detail. JPA Queries with JPQL We can get the number of Point objects in the database by using a simple query: Query q1 = em.createQuery("SELECT COUNT(p) FROM Point p"); System.out.println("Total Points: " + q1.getSingleResult()); The query string ("SELECT
Manual
66

WHERE clause (JPQL / Criteria API)

JPQL query that retrieves selective objects from the database. Out of the four optional clauses of JPQL queries, the WHERE clause is definitely the most frequently used. How a WHERE Clause Works The following query retrieves only countries with population size that exceeds a specified limit
Manual
63

Index Definition

Querying without indexes requires iteration over entity objects in the database one by ... the iteration can be avoided and complex queries over millions of objects can be executed quickly ... ; : } Indexes in Queries ObjectDB manages a BTree for every index. A BTree is an ordered map data structure
Manual
62

Database Management Settings

" synchronized="false" />    <query-cache results ... " operations (which modify the database) have to be recorded. For debugging of query failure ... execution of relevant queries. The <query-cache> element <query-cache results="32mb" programs="500
Manual
62

ORDER BY clause (JPQL / Criteria API)

The ORDER BY clause specifies a required order for the query results. Any JPQL query that does not ... Expressions The following query returns names of countries whose population size ... directly from expressions in the SELECT clause are allowed in the ORDER BY clause. The following query