title: Trying to explode an array with unnest() in Presto and failing due to extra column
body: <p>I have data from a query that looks like this: </p>
  
  <pre class="lang-sql prettyprint-override"><code>SELECT
      model_features
  FROM some_db
  </code></pre>
  
  <p>which returns: </p>
  
  <pre><code>{
    "food1": 0.65892159938812,
    "food2": 0.90786880254745,
    "food3": 0.88357985019684,
    "food4": 0.99999821186066,
    "food5": 0.99237471818924,
    "food6": 0.62127977609634
  }
  {
    "food4": 0.9999965429306,
    "text1": 0.82206630706787
  }
  ...
  </code></pre>
  
  <p>etc. </p>
  
  <p>What I am eventually trying to do is simply get a count of each of the "food1", "food2" features,
  but to do so (i <em>think</em>) I need to trim out the unnecessary numeric data. I'm at a loss as to how to do this, as everytime I try to simply unnest </p>
  
  <pre class="lang-sql prettyprint-override"><code>SELECT
      t.concepts
  FROM some_db
  CROSS JOIN UNNEST(model_features) AS t(concepts)
  </code></pre>
  
  <p>I get this error:</p>
  
  <p><code>Column alias list has 1 entries but 't' has 2 columns available</code></p>
  
  <p>Anyone mind pointing me in the right direction? </p>