title: Extracting JSON with common_schema
body: <p>I truly hope there is someone here who is savvy with common_schema plug-in to MySQL, which should be built on xpath.
  I have a json that looks like so </p>
  
  <p><code>set @json:= '{"349724":{"id1":349724,"id":"14005","level":30,"up":141427}}'</code></p>
  
  <p>I am writing this </p>
  
  <p><code>SELECT common_schema.extract_json_value(@json, '/349724/id') AS result ;</code></p>
  
  <p>Error Code: 1105. XPATH syntax error: '349724/id'</p>
  
  <p>Could you point me to the right direction here?
  To me this example look totally the same as this one.
  <a href="https://common-schema.googlecode.com/svn/trunk/common_schema/doc/html/extract_json_value.html" rel="nofollow">https://common-schema.googlecode.com/svn/trunk/common_schema/doc/html/extract_json_value.html</a></p>
  
  <p>using json_to_xml() returns this
  <code>&lt;349724&gt;&lt;id1&gt;349724&lt;/id1&gt;&lt;id&gt;14005&lt;/id&gt;&lt;level&gt;30&lt;/level&gt;&lt;up&gt;141427&lt;/up&gt;&lt;/349724&gt;</code></p>
  
  <p>This is the snippet of the code for extract_json_value() method.</p>
  
  <p><code>create function extract_json_value(
         json_text text charset utf8,
         xpath text charset utf8
      ) returns text charset utf8
      comment 'Extracts JSON value via XPath'
      language SQL
      deterministic
      modifies sql data
      sql security invoker
      begin
        return ExtractValue(json_to_xml(json_text), xpath);<br>
      end;</code></p>