// WHERE name = 'dogstar' AND age = 18
$user->where(array('name' => 'dogstar', 'age' => 18))
// WHERE name = 'dogstar' OR age = 18
$user->or('name', 'dogstar')->or('age', 18)
// WHERE ((name = ? OR id = ?)) AND (note = ?) -- 'dogstar', '1', 'xxx'
#实现方式1：使用and拼接
$user->where('(name = ? OR id = ?)', 'dogstar', '1')->and('note = ?', 'xxx')
#实现方式2：只使用where，不用数组传参
$user->where('(name = ? OR id = ?) AND note = ?', 'dogstar', '1', 'xxx')
#实现方式3：只使用where，用下标为顺序数字的数组传参
$user->where('(name = ? OR id = ?) AND note = ?', array('dogstar', '1', 'xxx'))
#实现方式4：只使用where，用下标为标识符的数组传参
$user->where('(name = :name OR id = :id) AND note = :note', array(':name' => 'dogstar', ':id' => '1', ':note' => 'xxx'))
