system/Database/SQLite3/Forge.php
protected function _alterTable(string $alter_type, string $table, $field)
	{
		switch ($alter_type)
		{
			case 'DROP':
				$sqlTable = new Table($this->db, $this);

				$sqlTable->fromTable($table)
					->dropColumn($field)
					->run();

				return '';
				break;
			case 'CHANGE':
				$sqlTable = new Table($this->db, $this);

				$sqlTable->fromTable($table)
						 ->modifyColumn($field)
						 ->run();

				return null;
				break;
			default:
				return parent::_alterTable($alter_type, $table, $field);
		}
	}
protected function _alterTable(string $alter_type, string $table, $field)
	{
		switch ($alter_type)
		{
			case 'DROP':
				$sqlTable = new Table($this->db, $this);

				$sqlTable->fromTable($table)
					->dropColumn($field)
					->run();

				return '';
				break;
			case 'CHANGE':
				$sqlTable = new Table($this->db, $this);

				$sqlTable->fromTable($table)
						 ->modifyColumn($field)
						 ->run();

				return null;
				break;
			default:
				return parent::_alterTable($alter_type, $table, $field);
		}
	}
ALTER TABLE

@param string $alter_type ALTER type
@param string $table      Table name
@param mixed  $field      Column definition

@return string|array