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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
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<title>6.18. Map Functions and Operators — Presto 0.154 Documentation</title>
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<div class="header">
<h1 class="heading"><a href="../index.html">
<span>Presto 0.154 Documentation</span></a></h1>
<h2 class="heading"><span>6.18. Map Functions and Operators</span></h2>
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<div class="section" id="map-functions-and-operators">
<h1>6.18. Map Functions and Operators</h1>
<div class="section" id="subscript-operator">
<h2>Subscript Operator: []</h2>
<p>The <code class="docutils literal"><span class="pre">[]</span></code> operator is used to retrieve the value corresponding to a given key from a map:</p>
<div class="highlight-sql"><div class="highlight"><pre><span></span><span class="k">SELECT</span> <span class="n">name_to_age_map</span><span class="p">[</span><span class="s1">'Bob'</span><span class="p">]</span> <span class="k">AS</span> <span class="n">bob_age</span><span class="p">;</span>
</pre></div>
</div>
</div>
<div class="section" id="map-functions">
<h2>Map Functions</h2>
<dl class="function">
<dt>
<code class="descname">cardinality</code><span class="sig-paren">(</span><em>x</em><span class="sig-paren">)</span> → bigint</dt>
<dd><p>Returns the cardinality (size) of the map <code class="docutils literal"><span class="pre">x</span></code>.</p>
</dd></dl>
<dl class="function">
<dt>
<code class="descname">element_at</code><span class="sig-paren">(</span><em>map<K</em>, <em>V></em>, <em>key</em><span class="sig-paren">)</span> → V</dt>
<dd><p>Returns value for given <code class="docutils literal"><span class="pre">key</span></code>, or <code class="docutils literal"><span class="pre">NULL</span></code> if the key is not contained in the map.</p>
</dd></dl>
<dl class="function">
<dt id="map">
<code class="descname">map</code><span class="sig-paren">(</span><em>array<K></em>, <em>array<V></em><span class="sig-paren">)</span> → map<K,V></dt>
<dd><p>Returns a map created using the given key/value arrays.</p>
<div class="highlight-sql"><div class="highlight"><pre><span></span><span class="k">SELECT</span> <span class="k">map</span><span class="p">(</span><span class="nb">ARRAY</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">],</span> <span class="nb">ARRAY</span><span class="p">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">]);</span> <span class="c1">-- {1 -> 2, 3 -> 4}</span>
</pre></div>
</div>
<p>See also <a class="reference internal" href="aggregate.html#map_agg" title="map_agg"><code class="xref py py-func docutils literal"><span class="pre">map_agg()</span></code></a> and <a class="reference internal" href="aggregate.html#multimap_agg" title="multimap_agg"><code class="xref py py-func docutils literal"><span class="pre">multimap_agg()</span></code></a> for creating a map as an aggregation.</p>
</dd></dl>
<dl class="function">
<dt id="map_concat">
<code class="descname">map_concat</code><span class="sig-paren">(</span><em>x<K</em>, <em>V></em>, <em>y<K</em>, <em>V></em><span class="sig-paren">)</span> → map<K,V></dt>
<dd><p>Returns the union of two maps. If a key is found in both <code class="docutils literal"><span class="pre">x</span></code> and <code class="docutils literal"><span class="pre">y</span></code>,
that key’s value in the resulting map comes from <code class="docutils literal"><span class="pre">y</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="map_keys">
<code class="descname">map_keys</code><span class="sig-paren">(</span><em>x<K</em>, <em>V></em><span class="sig-paren">)</span> → array<K></dt>
<dd><p>Returns all the keys in the map <code class="docutils literal"><span class="pre">x</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="map_values">
<code class="descname">map_values</code><span class="sig-paren">(</span><em>x<K</em>, <em>V></em><span class="sig-paren">)</span> → array<V></dt>
<dd><p>Returns all the values in the map <code class="docutils literal"><span class="pre">x</span></code>.</p>
</dd></dl>
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