title: How do I use BigQuery patch?
body: <p>In the BigQuery API documentation there is a method called patch.  I am hoping that I can use it to alter the schema of an existing table.  Unfortunately it is not supported by bq.  But according to their website, you can try it at <a href="https://developers.google.com/bigquery/docs/reference/v2/tables/patch" rel="noreferrer">https://developers.google.com/bigquery/docs/reference/v2/tables/patch</a>.  However when I try it sends the following request:</p>
  
  <pre><code>PATCH https://www.googleapis.com/bigquery/v2/projects/(my project id)/datasets/tmp_bt/tables/change_cols?key={YOUR_API_KEY}
  
  Content-Type:  application/json
  Authorization:  Bearer (removed)
  X-JavaScript-User-Agent:  Google APIs Explorer
  
  {
   "schema": {
    "fields": [
     {
     },
     {
     },
     {
      "mode": "nullable",
      "name": "gotchahere",
      "type": "string"
     }
    ]
   }
  }
  </code></pre>
  
  <p>(I have no idea where the empty elements came from, and the editor is too painful to use to just paste in my existing table definition.  I note that it is missing required elements like my project ID, which I expected to be included because they were required in the form) and then I get the response:</p>
  
  <pre><code>cache-control:  private, max-age=0
  content-encoding:  gzip
  content-length:  122
  content-type:  application/json; charset=UTF-8
  date:  Thu, 13 Jun 2013 22:22:09 GMT
  expires:  Thu, 13 Jun 2013 22:22:09 GMT
  server:  GSE
  
  {
   "error": {
    "errors": [
     {
      "domain": "global",
      "reason": "backendError",
      "message": "Backend Error"
     }
    ],
    "code": 503,
    "message": "Backend Error"
   }
  }
  </code></pre>
  
  <p>which is utterly useless.  I've done a web search, and failed to find any examples of it in use.</p>
  
  <p>Can anyone give me an example of using BigQuery patch to alter a table, and a description of what it can actually do?</p>