title: Update field in one table using data from another based on a key value
body: <p>I need to update the Notes field in my table tblMain by concatenating the text data with the Notes field in my secondary table tblSecond by matching the ID field in both tables.</p>
  
  <p>I was using the following SQL:</p>
  
  <pre><code>UPDATE tblMain
  SET tblMain.Notes = (tblMain.Notes + (SELECT DISTINCT Notes FROM tblSecond
  WHERE tblSecond.ID = tblMain.ID))
  </code></pre>
  
  <p>but I get the following error</p>
  
  <blockquote>
    <p>Subquery returned more than 1 value.</p>
  </blockquote>
  
  <p>presumably because the SELECT statement is returning an entire resultset.</p>
  
  <p>How would I perform this operation successfully?</p>