re class="sourceCode r"><code><span><span class="fu">columns_used</span><span class="op">(</span><span class="va">x</span>, <span class="va">...</span>, using <span class="op">=</span> <span class="cn">NULL</span><span class="op">)</span></span></code></pre></div>
    </div>

    <div id="arguments">
    <h2>Arguments</h2>
    <dl><dt>x</dt>
<dd><p>rquery operation tree.</p></dd>


<dt>...</dt>
<dd><p>generic additional arguments (not used)</p></dd>


<dt>using</dt>
<dd><p>character, if not NULL set of colu