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 	<h1 class="title topictitle1" id="ariaid-title1">SELECT Clause</h1>


 	<div class="body refbody"><p class="shortdesc"></p>

 		<div class="section">
 			<p class="p">
 				The <code class="ph codeph">SELECT</code> clause determines what to extract from the
 				heap dump. To display objects and be able to browse the
 				outgoing references, use the
 				<code class="ph codeph">*</code>
 				symbol:
 			</p>

 			<pre class="pre codeblock"><code>SELECT * FROM java.lang.String</code></pre>

 			<p class="p"><strong class="ph b">Select specific columns</strong></p>

 			<p class="p">
 				Alternatively, one can select the fields to be
 				displayed:
 			</p>

 			<pre class="pre codeblock"><code>SELECT toString(s), s.count, s.value FROM java.lang.String s</code></pre>
 			<p class="p">
 				The resulting table knows about the underlying object.
 				So you can use the context menu to open further views on
 				the object at hand. Use the <code class="ph codeph">@</code> symbol to access Java
 				attributes and methods of the objects. There are also a
 				number of built-in functions available to extract common
 				information:
 			</p>

 			<pre class="pre codeblock"><code>SELECT toString(s), s.@usedHeapSize,
     s.@retainedHeapSize FROM java.lang.String s</code></pre>
 			<p class="p">
 				The section on
 				<a class="xref" href="propertyaccessors.html">
 					Property Accessors
 				</a>
 				contains details on the commonly available attributes.
 			</p>

 			<p class="p"><strong class="ph b">Provide column names</strong></p>

 			<p class="p">Use the AS keyword to name the columns:</p>

 			<pre class="pre codeblock"><code>SELECT toString(s) AS Value,
     s.@usedHeapSize AS "Shallow Size",
     s.@retainedHeapSize AS "Retained Size"
 			FROM java.lang.String s</code></pre>
 			<p class="p">
 				Use the
 				<code class="ph codeph">AS RETAINED SET</code>
 				keyword to get the set of objects retained by your
 				selection:
 			</p>

 			<pre class="pre codeblock"><code>SELECT AS RETAINED SET * FROM java.lang.String</code></pre>
 			<p class="p"><strong class="ph b">Flatten select items into an object list</strong></p>

 			<p class="p">
 				Use the
 				<code class="ph codeph">OBJECTS</code>
 				to interpret the items in the
 				<code class="ph codeph">SELECT</code>
 				clause as objects:
 			</p>

 			<pre class="pre codeblock"><code>SELECT OBJECTS dominators(s) FROM java.lang.String s</code></pre>
 			<p class="p">
 				The function
 				<code class="ph codeph">dominators()</code>
 				returns an array of objects. Therefore the query returns
 				a list of object lists, i.e. arrays. By using the
 				keyword
 				<code class="ph codeph">OBJECTS</code>
 				, we force the OQL to reduce this into a single list of
 				objects.
 			</p>

 			<p class="p"><strong class="ph b">Select unique objects</strong></p>

 			<p class="p">
 				Use the
 				<code class="ph codeph">DISTINCT</code>
 				keyword to only select unique objects:
 			</p>

 			<pre class="pre codeblock"><code>SELECT DISTINCT * FROM OBJECTS 0,1,1,2</code></pre>
 			<p class="p">
 				Use the
 				<code class="ph codeph">DISTINCT OBJECTS</code>
 				keyword to only select unique objects from the result of the selected clause:
 			</p>

 			<pre class="pre codeblock"><code>SELECT DISTINCT OBJECTS classof(s) FROM java.lang.String s</code></pre>
 			<p class="p">
 				The function
 				<code class="ph codeph">classof</code>
 				returns the class object. Of course, all Strings have
 				the same class. The <code class="ph codeph">OBJECTS</code> converts the underlying row with a String object
 				and a displayed value of the class object
 				to the object represented by the result of the <code class="ph codeph">classof</code> function.
 				Without the <code class="ph codeph">DISTINCT OBJECTS</code>
 				keywords, the query would result in a list with as many
 				rows with the same class as there are Strings.
 			</p>

 			<p class="p">With Memory Analyzer 1.10 or later, <code class="ph codeph">DISTINCT</code> also operates without
 			<code class="ph codeph">OBJECTS</code> to find items which are distinct.
 			See <a class="xref" href="https://wiki.eclipse.org/MemoryAnalyzer/OQL#SELECT_DISTINCT">Wiki: OQL SELECT DISTINCT</a>
 			for further details.</p>

 			<p class="p"><strong class="ph b">Expressions (experimental, Memory Analyzer 1.4 or later)</strong></p>

 			<p class="p">
 				Use the expressions for the select item, including string concatenation:
 			</p>

 			<pre class="pre codeblock"><code>SELECT s.@objectId, s.@objectId * 2, "The object ID is "+@objectId FROM OBJECTS 0,1,1,2 s</code></pre>
 			<p class="p">
 				With Memory Analyzer 1.4 or later expressions and sub-selects are allowed for select items. More complex
 				expressions may need to be parenthesized. This is currently in the test phase.
 			</p>

 		</div>

 	</div>

 <div class="related-links">
 <div class="familylinks">
 <div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../reference/oqlsyntax.html">OQL Syntax</a></div>
 </div>
 </div></body>
 </html>
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	<meta name="description" content="" />
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	<meta name="copyright" content="Copyright (c) 2008, 2023 SAP AG and others. All rights reserved. This program and the accompanying materials are made available under the terms of the Eclipse Public License 2.0 which accompanies this distribution, and is available at https://www.eclipse.org/legal/epl-2.0/ " type="primary" />
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	<title>SELECT Clause</title>
	</head>
	<body id="ref_oqlsyntaxselect">

	<h1 class="title topictitle1" id="ariaid-title1">SELECT Clause</h1>





	<div class="body refbody"><p class="shortdesc"></p>

	<div class="section">
	<p class="p">
	The <code class="ph codeph">SELECT</code> clause determines what to extract from the
	heap dump. To display objects and be able to browse the
	outgoing references, use the
	<code class="ph codeph">*</code>
	symbol:
	</p>

	<pre class="pre codeblock"><code>SELECT * FROM java.lang.String</code></pre>

	<p class="p"><strong class="ph b">Select specific columns</strong></p>

	<p class="p">
	Alternatively, one can select the fields to be
	displayed:
	</p>

	<pre class="pre codeblock"><code>SELECT toString(s), s.count, s.value FROM java.lang.String s</code></pre>
	<p class="p">
	The resulting table knows about the underlying object.
	So you can use the context menu to open further views on
	the object at hand. Use the <code class="ph codeph">@</code> symbol to access Java
	attributes and methods of the objects. There are also a
	number of built-in functions available to extract common
	information:
	</p>

	<pre class="pre codeblock"><code>SELECT toString(s), s.@usedHeapSize,
	s.@retainedHeapSize FROM java.lang.String s</code></pre>
	<p class="p">
	The section on
	<a class="xref" href="propertyaccessors.html">
	Property Accessors
	</a>
	contains details on the commonly available attributes.
	</p>

	<p class="p"><strong class="ph b">Provide column names</strong></p>

	<p class="p">Use the AS keyword to name the columns:</p>

	<pre class="pre codeblock"><code>SELECT toString(s) AS Value,
	s.@usedHeapSize AS "Shallow Size",
	s.@retainedHeapSize AS "Retained Size"
	FROM java.lang.String s</code></pre>
	<p class="p">
	Use the
	<code class="ph codeph">AS RETAINED SET</code>
	keyword to get the set of objects retained by your
	selection:
	</p>

	<pre class="pre codeblock"><code>SELECT AS RETAINED SET * FROM java.lang.String</code></pre>
	<p class="p"><strong class="ph b">Flatten select items into an object list</strong></p>

	<p class="p">
	Use the
	<code class="ph codeph">OBJECTS</code>
	to interpret the items in the
	<code class="ph codeph">SELECT</code>
	clause as objects:
	</p>

	<pre class="pre codeblock"><code>SELECT OBJECTS dominators(s) FROM java.lang.String s</code></pre>
	<p class="p">
	The function
	<code class="ph codeph">dominators()</code>
	returns an array of objects. Therefore the query returns
	a list of object lists, i.e. arrays. By using the
	keyword
	<code class="ph codeph">OBJECTS</code>
	, we force the OQL to reduce this into a single list of
	objects.
	</p>

	<p class="p"><strong class="ph b">Select unique objects</strong></p>

	<p class="p">
	Use the
	<code class="ph codeph">DISTINCT</code>
	keyword to only select unique objects:
	</p>

	<pre class="pre codeblock"><code>SELECT DISTINCT * FROM OBJECTS 0,1,1,2</code></pre>
	<p class="p">
	Use the
	<code class="ph codeph">DISTINCT OBJECTS</code>
	keyword to only select unique objects from the result of the selected clause:
	</p>

	<pre class="pre codeblock"><code>SELECT DISTINCT OBJECTS classof(s) FROM java.lang.String s</code></pre>
	<p class="p">
	The function
	<code class="ph codeph">classof</code>
	returns the class object. Of course, all Strings have
	the same class. The <code class="ph codeph">OBJECTS</code> converts the underlying row with a String object
	and a displayed value of the class object
	to the object represented by the result of the <code class="ph codeph">classof</code> function.
	Without the <code class="ph codeph">DISTINCT OBJECTS</code>
	keywords, the query would result in a list with as many
	rows with the same class as there are Strings.
	</p>

	<p class="p">With Memory Analyzer 1.10 or later, <code class="ph codeph">DISTINCT</code> also operates without
	<code class="ph codeph">OBJECTS</code> to find items which are distinct.
	See <a class="xref" href="https://wiki.eclipse.org/MemoryAnalyzer/OQL#SELECT_DISTINCT">Wiki: OQL SELECT DISTINCT</a>
	for further details.</p>

	<p class="p"><strong class="ph b">Expressions (experimental, Memory Analyzer 1.4 or later)</strong></p>

	<p class="p">
	Use the expressions for the select item, including string concatenation:
	</p>

	<pre class="pre codeblock"><code>SELECT s.@objectId, s.@objectId * 2, "The object ID is "+@objectId FROM OBJECTS 0,1,1,2 s</code></pre>
	<p class="p">
	With Memory Analyzer 1.4 or later expressions and sub-selects are allowed for select items. More complex
	expressions may need to be parenthesized. This is currently in the test phase.
	</p>

	</div>

	</div>

	<div class="related-links">
	<div class="familylinks">
	<div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../reference/oqlsyntax.html">OQL Syntax</a></div>
	</div>
	</div></body>
	</html>