Driver_Database_Driver_MySQL::_quote_identifier

protected function _quote_identifier($column)
{
    if (is_array($column))
    {
        list($column, $alias) = $column;
    }

    if (is_object($column))
    {
        if ($column instanceof Database)
        {
            // Create a sub-query
            $column = '(' . $column->compile() . ')';
        }
        elseif ($column instanceof Database_Expression)
        {
            // Use a raw expression
            $column = $column->value();
        }
        else
        {
            // Convert the object to a string
            $column = $this->_quote_identifier((string)$column);
        }
    }
    else
    {
 转换为字符串
        $column = trim((string)$column);

        if (preg_match('#^(.*) AS (.*)$#i', $column, $m))
        {
            $column = $m[1];
            $alias  = $m[2];
        }

        if ($column === '*')
        {
            return $column;
        }
        elseif (strpos($column, '"') !== false)
        {
            // Quote the column in FUNC("column") identifiers
            $column = preg_replace('/"(.+?)"/e', '$this->_quote_identifier("$1")', $column);
        }
        elseif (strpos($column, '.') !== false)
        {
            $parts = explode('.', $column);

            $prefix = $this->config['table_prefix'];
            if ($prefix)
            {
                // Get the offset of the table name, 2nd-to-last part
                $offset = count($parts) - 2;

                if (!$this->_as_table || !in_array($parts[$offset], $this->_as_table))
                {
                    $parts[$offset] = $prefix . $parts[$offset];
                }
            }

            foreach ($parts as & $part)
            {
                if ($part !== '*')
                {
                    // Quote each of the parts
	    $this->_change_charset($part);
		$part = $this->_identifier . str_replace($this->_identifier, '', $part) . $this->_identifier;
                }
            }

            $column = implode('.', $parts);
        }
        else
        {
   $this->_change_charset($column);
$column = $this->_identifier . str_replace($this->_identifier, '', $column) . $this->_identifier;
        }
    }

    if (isset($alias))
    {
  $this->_change_charset($alias);
column .= ' AS ' . $this->_identifier . str_replace($this->_identifier, '', $alias) . $this->_identifier;
    }

    return $column;
}