title: Import CSV to Update only one column in table
body: <p>I have a table that looks like this:</p>
  
  <pre><code>products
  --------
  id, product, sku, department, quantity
  </code></pre>
  
  <p>There are approximately 800,000 entries in this table. I have received a new CSV file that updates all of the quantities of each product, for example:</p>
  
  <pre><code>productA, 12
  productB, 71
  productC, 92
  </code></pre>
  
  <p>So there are approximately 750,000 updates (50,000 products had no change in quantity).</p>
  
  <p>My question is, how do I import this CSV to update only the quantity based off of the <code>product</code> (unique) but leave the <code>sku</code>, <code>department</code>, and other fields alone? I know how to do this in PHP by looping through the CSV and executing an update for each single line but this seems inefficient.</p>