title: Snowflake External Table : Add new column
body: <p>I created a snowflake external table successfully and was able to load the data from s3. I want to add a column to this external table. In the Snowflake documentation they say that - 
  "Alter an existing external table to add or remove columns using the following ALTER TABLE syntax:
  Add columns: ALTER TABLE … ADD COLUMN.
  Remove columns: ALTER TABLE … DROP COLUMN."</p>
  
  <p>When I try adding a column to my external table, it gives me following error -
  "External table column TEST_COL must have a defining expression."</p>
  
  <p>I am using following command to add the column - 
  alter table EXTTABLE_TEST add column TEST_COL number;</p>
  
  <p>Here is the link to Snowflake Documentation I am referring to - <a href="https://docs.snowflake.net/manuals/user-guide/tables-external-intro.html#adding-or-dropping-columns" rel="nofollow noreferrer">https://docs.snowflake.net/manuals/user-guide/tables-external-intro.html#adding-or-dropping-columns</a></p>
  
  <p>Can someone please help me with this? Is it even possible to add/remove columns from external table.
  Any help is appreciated.</p>
  
  <p>Thanks!</p>