title: Query in Spark SQL inside an array
body: <p>To give the backfround I have loaded the JSON using</p>
  
  <pre><code>sqlContext.read.json(sn3://...)
  df.registerTable("posts")
  </code></pre>
  
  <p>I have the following schema for my table in Spark</p>
  
  <pre><code>scala&gt; posts.printSchema
  root
   |-- command: string (nullable = true)
   |-- externalId: string (nullable = true)
   |-- sourceMap: struct (nullable = true)
   |    |-- hashtags: array (nullable = true)
   |    |    |-- element: string (containsNull = true)
   |    |-- url: string (nullable = true)
   |-- type: string (nullable = true)
  </code></pre>
  
  <p>I want to select all posts with hashtag "nike"</p>
  
  <pre><code>sqlContext.sql("select sourceMap['hashtags'] as ht from posts where ht.contains('nike')");
  </code></pre>
  
  <p>I get an error 
  undefined function ht.contains</p>
  
  <p>I am not sure what method to use to search within the array.</p>
  
  <p>Thanks!</p>