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  <div class="section" id="setnx">
<span id="id1"></span><h1>SETNX<a class="headerlink" href="#setnx" title="Permalink to this headline">¶</a></h1>
<p><strong>SETNX key value</strong></p>
<p>将 <code class="docutils literal"><span class="pre">key</span></code> 的值设为 <code class="docutils literal"><span class="pre">value</span></code> ，当且仅当 <code class="docutils literal"><span class="pre">key</span></code> 不存在。</p>
<p>若给定的 <code class="docutils literal"><span class="pre">key</span></code> 已经存在，则 <a class="reference internal" href="#setnx">SETNX</a> 不做任何动作。</p>
<p><a class="reference internal" href="#setnx">SETNX</a> 是『SET if Not eXists』(如果不存在，则 SET)的简写。</p>
<dl class="docutils">
<dt><strong>可用版本：</strong></dt>
<dd>&gt;= 1.0.0</dd>
<dt><strong>时间复杂度：</strong></dt>
<dd>O(1)</dd>
<dt><strong>返回值：</strong></dt>
<dd><div class="first last line-block">
<div class="line">设置成功，返回 <code class="docutils literal"><span class="pre">1</span></code> 。</div>
<div class="line">设置失败，返回 <code class="docutils literal"><span class="pre">0</span></code> 。</div>
</div>
</dd>
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<div class="highlight-python"><div class="highlight"><pre>redis&gt; EXISTS job                # job 不存在
(integer) 0

redis&gt; SETNX job &quot;programmer&quot;    # job 设置成功
(integer) 1

redis&gt; SETNX job &quot;code-farmer&quot;   # 尝试覆盖 job ，失败
(integer) 0

redis&gt; GET job                   # 没有被覆盖
&quot;programmer&quot;
</pre></div>
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