Understanding EclipseLink, 2.4
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About Oracle Extensions for Queries

When you use EclipseLink with Oracle Database, you can make use of the following Oracle-specific query features from within your EclipseLink applications:

Query Hints

Oracle lets you specify SQL query additions called hints that can influence how the database server SQL optimizer works. This lets you influence decisions usually reserved for the optimizer. You use hints to specify things such as join order for a join statement, or the optimization approach for a SQL call.

You specify hints using the DatabaseQuery method setHintString.

For more information, see the performance tuning guide for your database.

Hierarchical Queries

Oracle Database Hierarchical Queries mechanism lets you select database rows based on hierarchical order. For example, you can design a query that reads the row of a given employee, followed by the rows of people the employee manages, followed by their managed employees, and so on.

You specify a hierarchical query clause using DatabaseQuery subclass ReadAllQuery method setHierarchicalQueryClause.

Flashback Queries

When using EclipseLink with Oracle9i Database (or later), you can acquire a special historical session where all objects are read as of a past time, and then you can express read queries depending on how your objects are changing over time.

Stored Functions

A stored function is an Oracle Database mechanism that provides all the capabilities of a stored procedure in addition to returning a value.