title: How to convert json string datatype column to map datatype column in hive?
body: <p><a href="https://i.stack.imgur.com/QvO0B.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QvO0B.png" alt="enter image description here"></a></p>
  
  <p><strong>I need to get all the unique key values from all the rows</strong>. <strong>Each row has different keys and values</strong> Please find the above image of the column.</p>
  
  <p>eg: one row looks like </p>
  
  <pre><code>{"START_TIME":1549002807568,"PARSING.QUERY_FORMED":1549002807586,"CUBES_WITH_PERMISSIONS":1549002807568,"PARSING.CUBE_MATCH_SELECTED":1549002807586,"POTENTIAL_COMPLETIONS_ADDED":1549002807587,"QUERY_PARSED":1549002807586,"SUGGESTIONS_FORMED":1549002807606,"PARSING.SEQUENCES_GENERATED":1549002807568,"PARSING.NGRAM_MATCHES_CACHED":1549002807585}
  </code></pre>