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<div class="sub-title"><span class="package-label-in-type">Package</span>&nbsp;<a href="package-summary.html">org.apache.datafusion</a></div>
<h1 title="Interface ScalarFunction" class="title">Interface ScalarFunction</h1>
</div>
<section class="class-description" id="class-description">
<hr>
<div class="type-signature"><span class="modifiers">public interface </span><span class="element-name type-name-label">ScalarFunction</span></div>
<div class="block">A Java-implemented scalar SQL function. Implementations declare their own name, signature, and
 volatility, and evaluate one input batch at a time.

 <p>Mirrors DataFusion's <code>ScalarUDFImpl</code> trait. Wrap an instance in a <a href="ScalarUdf.html" title="class in org.apache.datafusion"><code>ScalarUdf</code></a> and
 register it via <a href="SessionContext.html#registerUdf(org.apache.datafusion.ScalarUdf)"><code>SessionContext.registerUdf(ScalarUdf)</code></a> to make it callable from SQL or
 DataFrame plans.

 <p>Implementations may be invoked concurrently by DataFusion on multiple worker threads. If the
 implementation carries mutable state, the implementation must synchronize it.</div>
</section>
<section class="summary">
<ul class="summary-list">
<!-- ========== METHOD SUMMARY =========== -->
<li>
<section class="method-summary" id="method-summary">
<h2>Method Summary</h2>
<div id="method-summary-table">
<div class="table-tabs" role="tablist" aria-orientation="horizontal"><button id="method-summary-table-tab0" role="tab" aria-selected="true" aria-controls="method-summary-table.tabpanel" tabindex="0" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table', 3)" class="active-table-tab">All Methods</button><button id="method-summary-table-tab2" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab2', 3)" class="table-tab">Instance Methods</button><button id="method-summary-table-tab3" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab3', 3)" class="table-tab">Abstract Methods</button></div>
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<div class="summary-table three-column-summary">
<div class="table-header col-first">Modifier and Type</div>
<div class="table-header col-second">Method</div>
<div class="table-header col-last">Description</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/List.html" title="class or interface in java.util" class="external-link">List</a>&lt;org.apache.arrow.vector.types.pojo.Field&gt;</code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#argFields()" class="member-name-link">argFields</a>()</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Declared argument fields, in positional order.</div>
</div>
<div class="col-first odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="ColumnarValue.html" title="interface in org.apache.datafusion">ColumnarValue</a></code></div>
<div class="col-second odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#evaluate(org.apache.arrow.memory.BufferAllocator,org.apache.datafusion.ScalarFunctionArgs)" class="member-name-link">evaluate</a><wbr>(org.apache.arrow.memory.BufferAllocator&nbsp;allocator,
 <a href="ScalarFunctionArgs.html" title="class in org.apache.datafusion">ScalarFunctionArgs</a>&nbsp;args)</code></div>
<div class="col-last odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Compute the function result for one input batch.</div>
</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#name()" class="member-name-link">name</a>()</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">SQL name under which this function is invoked (e.g., <code>"add_one"</code>).</div>
</div>
<div class="col-first odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code>org.apache.arrow.vector.types.pojo.Field</code></div>
<div class="col-second odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#returnField()" class="member-name-link">returnField</a>()</code></div>
<div class="col-last odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Declared return field.</div>
</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="Volatility.html" title="enum class in org.apache.datafusion">Volatility</a></code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#volatility()" class="member-name-link">volatility</a>()</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Volatility classification.</div>
</div>
</div>
</div>
</div>
</section>
</li>
</ul>
</section>
<section class="details">
<ul class="details-list">
<!-- ============ METHOD DETAIL ========== -->
<li>
<section class="method-details" id="method-detail">
<h2>Method Details</h2>
<ul class="member-list">
<li>
<section class="detail" id="name()">
<h3>name</h3>
<div class="member-signature"><span class="return-type"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></span>&nbsp;<span class="element-name">name</span>()</div>
<div class="block">SQL name under which this function is invoked (e.g., <code>"add_one"</code>).</div>
</section>
</li>
<li>
<section class="detail" id="argFields()">
<h3>argFields</h3>
<div class="member-signature"><span class="return-type"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/List.html" title="class or interface in java.util" class="external-link">List</a>&lt;org.apache.arrow.vector.types.pojo.Field&gt;</span>&nbsp;<span class="element-name">argFields</span>()</div>
<div class="block">Declared argument fields, in positional order. The function is registered with an exact
 signature; calls whose argument types do not match exactly are rejected.

 <p>Each entry is an Arrow <code>Field</code> -- a name plus a <code>FieldType</code> plus an optional
 list of child fields. Use <code>Field.nullable(String, org.apache.arrow.vector.types.pojo.ArrowType)</code> for primitive types (e.g. <code>
 Field.nullable("arg0", new ArrowType.Int(32, true))</code>). Nested types like <code>List</code>, <code>
 Struct</code>, and <code>Map</code> require the children list to carry element / member / key / value type
 information; constructing a <code>Field</code> via <code>new Field(name, FieldType, children)</code> is
 the canonical Arrow way to do that.</div>
</section>
</li>
<li>
<section class="detail" id="returnField()">
<h3>returnField</h3>
<div class="member-signature"><span class="return-type">org.apache.arrow.vector.types.pojo.Field</span>&nbsp;<span class="element-name">returnField</span>()</div>
<div class="block">Declared return field. The returned <a href="ColumnarValue.html" title="interface in org.apache.datafusion"><code>ColumnarValue</code></a>'s vector must have this exact type,
 including any nested children. Same construction rules as <a href="#argFields()"><code>argFields()</code></a>.</div>
</section>
</li>
<li>
<section class="detail" id="volatility()">
<h3>volatility</h3>
<div class="member-signature"><span class="return-type"><a href="Volatility.html" title="enum class in org.apache.datafusion">Volatility</a></span>&nbsp;<span class="element-name">volatility</span>()</div>
<div class="block">Volatility classification. Use <a href="Volatility.html#IMMUTABLE"><code>Volatility.IMMUTABLE</code></a> for pure functions, <a href="Volatility.html#STABLE"><code>Volatility.STABLE</code></a> for functions deterministic within a query, and <a href="Volatility.html#VOLATILE"><code>Volatility.VOLATILE</code></a>
 for non-deterministic functions.</div>
</section>
</li>
<li>
<section class="detail" id="evaluate(org.apache.arrow.memory.BufferAllocator,org.apache.datafusion.ScalarFunctionArgs)">
<h3>evaluate</h3>
<div class="member-signature"><span class="return-type"><a href="ColumnarValue.html" title="interface in org.apache.datafusion">ColumnarValue</a></span>&nbsp;<span class="element-name">evaluate</span><wbr><span class="parameters">(org.apache.arrow.memory.BufferAllocator&nbsp;allocator,
 <a href="ScalarFunctionArgs.html" title="class in org.apache.datafusion">ScalarFunctionArgs</a>&nbsp;args)</span></div>
<div class="block">Compute the function result for one input batch.</div>
<dl class="notes">
<dt>Parameters:</dt>
<dd><code>allocator</code> - the <code>BufferAllocator</code> that MUST be used for any new Arrow vector
     allocation, including the result. Buffers allocated from other allocators will not survive
     the JNI handoff.</dd>
<dd><code>args</code> - the per-arg <a href="ColumnarValue.html" title="interface in org.apache.datafusion"><code>ColumnarValue</code></a>s and the batch row count. Each <a href="ColumnarValue.html" title="interface in org.apache.datafusion"><code>ColumnarValue</code></a> is a read-only view; the implementation must NOT close its underlying
     vector.</dd>
<dt>Returns:</dt>
<dd>a <a href="ColumnarValue.html" title="interface in org.apache.datafusion"><code>ColumnarValue</code></a> of the declared return type. If <a href="ColumnarValue.Array.html" title="class in org.apache.datafusion"><code>ColumnarValue.Array</code></a>,
     the underlying vector must have length <code>args.rowCount()</code>; if <a href="ColumnarValue.Scalar.html" title="class in org.apache.datafusion"><code>ColumnarValue.Scalar</code></a>, length 1. Ownership of the returned vector transfers to the
     framework; the implementation must NOT close it.</dd>
</dl>
</section>
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