title: Oracle SQL Common Entries in two Columns
body: <p>I have a table that contains common entries in two columns.</p>
  
  <p>For Example:</p>
  
  <pre><code>Column1    Column2
  Entry1  || NULL  
  Entry2  || Entry1
  Entry3  || Entry1
  Entry4  || Entry4
  Entry5  || NULL
  </code></pre>
  
  <p>I want to find how many times the entries of column 1 appear in column 2.</p>
  
  <p>So the result would be something like:</p>
  
  <pre><code>Column1    Count
  Entry1  || 2
  Entry2  || 0
  Entry3  || 0
  Entry4  || 1
  Entry5  || 0
  </code></pre>