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        <span>Presto 0.123 Documentation</span></a></h1>
    <h2 class="heading"><span>5.16. Map Functions and Operators</span></h2>
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  <div class="section" id="map-functions-and-operators">
<h1>5.16. Map Functions and Operators</h1>
<div class="section" id="subscript-operator">
<h2>Subscript Operator: []</h2>
<p>The <tt class="docutils literal"><span class="pre">[]</span></tt> 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 class="k">SELECT</span> <span class="n">name_to_age_map</span><span class="p">[</span><span class="s1">&#39;Bob&#39;</span><span class="p">]</span> <span class="k">AS</span> <span class="n">bob_age</span>
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<div class="section" id="map-functions">
<h2>Map Functions</h2>
<dl class="function">
<dt id="map">
<tt class="descname">map</tt><big>(</big><em>array&lt;K&gt;</em>, <em>array&lt;V&gt;</em><big>)</big> &rarr; map&lt;K,V&gt;</dt>
<dd><p>Returns a map created using the given key/value arrays.</p>
<div class="highlight-sql"><pre>SELECT MAP(ARRAY[1,3], ARRAY[2,4]); =&gt; {1 -&gt; 2, 3 -&gt; 4}</pre>
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</dd></dl>

<dl class="function">
<dt>
<tt class="descname">cardinality</tt><big>(</big><em>x</em><big>)</big> &rarr; bigint</dt>
<dd><p>Returns the cardinality (size) of the map <tt class="docutils literal"><span class="pre">x</span></tt>.</p>
</dd></dl>

<dl class="function">
<dt id="map_keys">
<tt class="descname">map_keys</tt><big>(</big><em>x&lt;K</em>, <em>V&gt;</em><big>)</big> &rarr; array&lt;K&gt;</dt>
<dd><p>Returns all the keys in the map <tt class="docutils literal"><span class="pre">x</span></tt>.</p>
</dd></dl>

<dl class="function">
<dt id="map_values">
<tt class="descname">map_values</tt><big>(</big><em>x&lt;K</em>, <em>V&gt;</em><big>)</big> &rarr; array&lt;V&gt;</dt>
<dd><p>Returns all the values in the map <tt class="docutils literal"><span class="pre">x</span></tt>.</p>
</dd></dl>

<p>See also <a class="reference internal" href="aggregate.html#map_agg" title="map_agg"><tt class="xref py py-func docutils literal"><span class="pre">map_agg()</span></tt></a> and <a class="reference internal" href="aggregate.html#multimap_agg" title="multimap_agg"><tt class="xref py py-func docutils literal"><span class="pre">multimap_agg()</span></tt></a> for creating a map as an aggregation.</p>
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