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<div class="sect1">
<h1 class="sect1"><font face="arial, helvetica, sans-serif" color="#330099">About Advanced Native Query Support</font></h1>
<p>EclipseLink provides an expression framework (also known as <em>EclipseLink</em> <em>Native</em> <em>Query</em> <em>Support</em>) with which you can express queries in a database-neutral fashion as an alternative to SQL when writing queries not supported by JPQL. EclipseLink expressions offer the following advantages over SQL when you access a database:</p>
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<li>
<p>Expressions are easier to maintain because the database is abstracted.</p>
</li>
<li>
<p>Changes to descriptors or database tables do not affect the querying structures in the application.</p>
</li>
<li>
<p>Expressions enhance readability by standardizing the <code>Query</code> interface so that it looks similar to traditional Java calling conventions.</p>
</li>
<li>
<p>Expressions enable read queries to transparently query between two classes that share a relationship. If these classes are stored in multiple tables in the database, EclipseLink automatically generates the appropriate join statements to return information from both tables.</p>
</li>
<li>
<p>Expressions simplify complex operations.</p>
</li>
</ul>
<p>EclipseLink automatically generates the appropriate SQL from the specified expression.</p>
<p>The expression framework lets you work with expressions, database queries, call objects, and native queries.</p>
<ul>
<li>
<p>JPA Query Using a EclipseLink <code>DatabaseQuery</code></p>
<p>EclipseLink <code>DatabaseQuery</code> is a query object that provides a robust API for handling a variety of database query requirements, including reading and writing at the object level and at the data level.</p>
</li>
<li>
<p>JPA Query Using a EclipseLink Call Object</p>
<p>Using the <code>DatabaseQuery</code> method <code>setCall</code>, you can define your own EclipseLink <code>Call</code> to accommodate a variety of data source options, such as SQL stored procedures and stored functions.</p>
</li>
<li>
<p>Named Parameters in a Native Query</p>
<p>Using EclipseLink, you can specify a named parameter in a native query using the EclipseLink <code>#</code> convention.</p>
</li>
<li>
<p>JPQL Positional Parameters in a Native Query</p>
<p>Using EclipseLink, you can specify positional parameters in a native query using the Java Persistence Query Language (JPQL) positional parameter <code>?n</code> convention to specify a parameter by number.</p>
</li>
<li>
<p>JDBC-Style Positional Parameters in a Native Query</p>
<p>Using EclipseLink, you can specify positional parameters in a native query using the JDBC-style positional parameter <code>?</code> convention.</p>
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