title: update query in Spark SQL
body: <p>I wonder can I use the update query in sparksql just like:</p>
  
  <pre><code>sqlContext.sql("update users set name = '*' where name is null")
  </code></pre>
  
  <p>I got the error:</p>
  
  <pre><code>org.apache.spark.sql.AnalysisException: 
  Unsupported language features in query:update users set name = '*' where name is null
  </code></pre>
  
  <p>If the sparksql does not support the update query or am i writing the code incorrectly?</p>