title: Checking if key exists in Presto value map
body: <p>I am new to Presto, and can't quite figure out how to check if a key is present in a map. When I run a <code>SELECT</code> query, this error message is returned:</p>
  
  <p><code>Key not present in map: element</code></p>
  
  <pre><code>SELECT value_map['element'] FROM
  mytable
  WHERE name = 'foobar'
  </code></pre>
  
  <p>Adding <code>AND contains(value_map, 'element')</code> does not work</p>
  
  <p>The data type is a string array</p>
  
  <pre><code>SELECT typeof('value_map') FROM mytable 
  </code></pre>
  
  <p>returns <code>varchar(9)</code></p>
  
  <p>How would I only select records where 'element' is present in the <code>value_map</code>? </p>