title: How do I convert an empty string into a numerical null in Access SQL_
body: <p>I want to populate a table with data from a staging table. The interesting column in the staging table has the datatype <code>text</code> but is otherwise filled with either values that are parsable as doubles or are the empty string (ie <code>"4.209"</code>, <code>"42"</code> or <code>""</code>). The according column in the destination table has the data type <code>double</code>.</p>
  
  <p>The SQL Statement I am executing is</p>
  
  <pre><code>insert into dest (.., theColumn, ... ) select ...., theColumn, .. from src
  </code></pre>
  
  <p>When I execute the statement (using ADO) I receive a <code>Data type mismatch in criteria expression</code> error).</p>
  
  <p>If I replace <code>theColumn</code> with <code>null</code>, it works without error. So, I figure I should somehow convert empty strings to <code>null</code>s. Is this possible?</p>