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  <div class="section" id="secondary-indexes">
<span id="id1"></span><h1>Secondary Indexes<a class="headerlink" href="#secondary-indexes" title="Permalink to this headline">¶</a></h1>
<p>CQL supports creating secondary indexes on tables, allowing queries on the table to use those indexes. A secondary index
is identified by a name defined by:</p>
<pre>
<strong id="grammar-token-index_name">index_name</strong> ::=  re('[a-zA-Z_0-9]+')
</pre>
<div class="section" id="create-index">
<span id="create-index-statement"></span><h2>CREATE INDEX<a class="headerlink" href="#create-index" title="Permalink to this headline">¶</a></h2>
<p>Creating a secondary index on a table uses the <code class="docutils literal"><span class="pre">CREATE</span> <span class="pre">INDEX</span></code> statement:</p>
<pre>
<strong id="grammar-token-create_index_statement">create_index_statement</strong> ::=  CREATE [ CUSTOM ] INDEX [ IF NOT EXISTS ] [ <a class="reference internal" href="#grammar-token-index_name"><code class="xref docutils literal"><span class="pre">index_name</span></code></a> ]
                                ON <a class="reference internal" href="ddl.html#grammar-token-table_name"><code class="xref docutils literal"><span class="pre">table_name</span></code></a> '(' <a class="reference internal" href="#grammar-token-index_identifier"><code class="xref docutils literal"><span class="pre">index_identifier</span></code></a> ')'
                                [ USING <a class="reference internal" href="definitions.html#grammar-token-string"><code class="xref docutils literal"><span class="pre">string</span></code></a> [ WITH OPTIONS = <a class="reference internal" href="types.html#grammar-token-map_literal"><code class="xref docutils literal"><span class="pre">map_literal</span></code></a> ] ]
<strong id="grammar-token-index_identifier">index_identifier      </strong> ::=  <a class="reference internal" href="ddl.html#grammar-token-column_name"><code class="xref docutils literal"><span class="pre">column_name</span></code></a>
                           | ( KEYS | VALUES | ENTRIES | FULL ) '(' <a class="reference internal" href="ddl.html#grammar-token-column_name"><code class="xref docutils literal"><span class="pre">column_name</span></code></a> ')'
</pre>
<p>For instance:</p>
<div class="highlight-cql"><div class="highlight"><pre><span></span><span class="k">CREATE</span> <span class="k">INDEX</span> <span class="n">userIndex</span> <span class="k">ON</span> <span class="n">NerdMovies</span> <span class="p">(</span><span class="k">user</span><span class="p">);</span>
<span class="k">CREATE</span> <span class="k">INDEX</span> <span class="k">ON</span> <span class="n">Mutants</span> <span class="p">(</span><span class="n">abilityId</span><span class="p">);</span>
<span class="k">CREATE</span> <span class="k">INDEX</span> <span class="k">ON</span> <span class="k">users</span> <span class="p">(</span><span class="k">keys</span><span class="p">(</span><span class="n">favs</span><span class="p">));</span>
<span class="k">CREATE</span> <span class="k">CUSTOM</span> <span class="k">INDEX</span> <span class="k">ON</span> <span class="k">users</span> <span class="p">(</span><span class="n">email</span><span class="p">)</span> <span class="k">USING</span> <span class="s1">&#39;path.to.the.IndexClass&#39;</span><span class="p">;</span>
<span class="k">CREATE</span> <span class="k">CUSTOM</span> <span class="k">INDEX</span> <span class="k">ON</span> <span class="k">users</span> <span class="p">(</span><span class="n">email</span><span class="p">)</span> <span class="k">USING</span> <span class="s1">&#39;path.to.the.IndexClass&#39;</span> <span class="k">WITH</span> <span class="k">OPTIONS</span> <span class="o">=</span> <span class="p">{</span><span class="s1">&#39;storage&#39;</span><span class="p">:</span> <span class="s1">&#39;/mnt/ssd/indexes/&#39;</span><span class="p">};</span>
</pre></div>
</div>
<p>The <code class="docutils literal"><span class="pre">CREATE</span> <span class="pre">INDEX</span></code> statement is used to create a new (automatic) secondary index for a given (existing) column in a
given table. A name for the index itself can be specified before the <code class="docutils literal"><span class="pre">ON</span></code> keyword, if desired. If data already exists
for the column, it will be indexed asynchronously. After the index is created, new data for the column is indexed
automatically at insertion time.</p>
<p>Attempting to create an already existing index will return an error unless the <code class="docutils literal"><span class="pre">IF</span> <span class="pre">NOT</span> <span class="pre">EXISTS</span></code> option is used. If it
is used, the statement will be a no-op if the index already exists.</p>
<div class="section" id="indexes-on-map-keys">
<h3>Indexes on Map Keys<a class="headerlink" href="#indexes-on-map-keys" title="Permalink to this headline">¶</a></h3>
<p>When creating an index on a <a class="reference internal" href="types.html#maps"><span class="std std-ref">maps</span></a>, you may index either the keys or the values. If the column identifier is
placed within the <code class="docutils literal"><span class="pre">keys()</span></code> function, the index will be on the map keys, allowing you to use <code class="docutils literal"><span class="pre">CONTAINS</span> <span class="pre">KEY</span></code> in
<code class="docutils literal"><span class="pre">WHERE</span></code> clauses. Otherwise, the index will be on the map values.</p>
</div>
</div>
<div class="section" id="drop-index">
<span id="drop-index-statement"></span><h2>DROP INDEX<a class="headerlink" href="#drop-index" title="Permalink to this headline">¶</a></h2>
<p>Dropping a secondary index uses the <code class="docutils literal"><span class="pre">DROP</span> <span class="pre">INDEX</span></code> statement:</p>
<pre>
<strong id="grammar-token-drop_index_statement">drop_index_statement</strong> ::=  DROP INDEX [ IF EXISTS ] <a class="reference internal" href="#grammar-token-index_name"><code class="xref docutils literal"><span class="pre">index_name</span></code></a>
</pre>
<p>The <code class="docutils literal"><span class="pre">DROP</span> <span class="pre">INDEX</span></code> statement is used to drop an existing secondary index. The argument of the statement is the index
name, which may optionally specify the keyspace of the index.</p>
<p>If the index does not exists, the statement will return an error, unless <code class="docutils literal"><span class="pre">IF</span> <span class="pre">EXISTS</span></code> is used in which case the
operation is a no-op.</p>
</div>
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