title: How to merge existing row with new data in SQLite?
body: <p>I have a database full of simple note data, with columns for title, due date, priority, and details.  There is also a _id column PRIMARY KEY int.</p>
  
  <p>Say I have a note in the table already with some data filled and the rest null.  I also have a set of data that will fill all those fields.</p>
  
  <p>Is there a way that I can only write data to the fields that are NULL?</p>
  
  <p>I can't overwrite existing data, but I'd like to add data to NULL columns.</p>
  
  <p>I know the rowId of the target row.</p>
  
  <p>If my target row had rowId of 5, I could do something like this:</p>
  
  <pre><code>UPDATE SET duedate='some date', priority='2', details='some text' WHERE _id=5
  </code></pre>
  
  <p>But that would overwrite all the data in that row, and I don't want to lose any data that might be there.  How can I change this statement to avoid writing to non-null fields?</p>