title: leave a column alone while replacing in mysql
body: <p>so suppose there's a table:</p>
  
  <pre><code>id column1 column2
  
   1   333     4444
  </code></pre>
  
  <p>Where id is a primary key</p>
  
  <p>And then I do</p>
  
  <pre><code>REPLACE INTO table (id, column2) VALUES (1, 55)
  </code></pre>
  
  <p>This will cause column1 to become null...is there a way to specify the query such that it will leave whatever existing value of column1 is when REPLACE matches an existing entry?</p>