docs: def add_comment(self, table, column, comment):
          """Add a comment to an existing column in a table."""
          col_def = self.get_column_definition(table, column)
          query = "ALTER TABLE {0} MODIFY COLUMN {1} {2} COMMENT '{3}'".format(table, column, col_def, comment)
          self.execute(query)
          self._printer('\tAdded comment to column {0}'.format(column))
          return True