title: Does DolphinDB support modifying the field type in a dfs table?
body: <p>I create a dfs table. The script is as below:</p>
  <pre class="lang-py prettyprint-override"><code>db = database(&quot;dfs://valuedb&quot;, VALUE, 2000.01M..2016.12M)
  schemaTable = table(1:0, `symbol`time`price, [STRING, TIMESTAMP, DOUBLE])
  pt = db.createPartitionedTable(schemaTable, `pt, `time)
  </code></pre>
  <p>Now, I want to modify the type of symbol from STRING to SYMBOL. Is there a ready-made function?</p>